A few peaceful days passed. The joint research between Akira and Tamayo progressed smoothly, far better than anyone expected.
Thanks to Tamayo's extensive knowledge of demon physiology and Akira's power of evolution, their studies advanced at an incredible pace. His unique ability allowed them to accelerate tests that would normally take months into mere days. Sure, his evolution power didn't always function exactly as intended, but he was growing more proficient with it by the day.
Tamayo looked up from her notes, genuinely impressed.
"Your power is extraordinary, Akira-san," she said with a gentle smile. "With this, our research may reach breakthroughs sooner than ever imagined."
Akira scratched his head modestly. "I can make it go even faster if I inject myself with Muzan's cells and build resistance against them."
Erika froze, her expression darkening. "I will literally murder you if you even think about that."
Akira chuckled awkwardly. "Right, right. I value my life too much to test that theory."
So under the very watchful eyes of a certain someone, their research continued safely.
Meanwhile, Erika's training in learning Blood Demon Arts wasn't going as smoothly.
Getting used to Akira's Mystic Eyes of Truth was proving far more difficult than expected. Her mind and body needed time to adjust to what those eyes could perceive, a world far too vivid and overwhelming for ordinary senses.
Still, thanks to Akira's Exp Overclock ability, she was making steady progress, albeit slowly.
One quiet night, Akira lay awake on his bed, staring at the ceiling. The faint sound of breathing from the other side of the room told him that Erika was sound asleep, peaceful as always.
But his mind refused to rest. Something had been bothering him for a while, something small, yet persistent enough to keep him awake.
After a few minutes of silent debate, he finally decided to ask the one person who could always hear him.
"Hey, sis," he called out telepathically.
Selena's calm, melodic voice answered in his mind. "What is it, brother?"
Akira hesitated for a moment before saying, "Tomorrow's Erika's birthday, right? What should I do about it?"
Selena's tone shifted to mild confusion. "Her birthday? What are you talking about? Her birthday is June 7th, and tomorrow is…"
"Yeah, I know," Akira interrupted, "but if you think about it, the time difference between this world and ours is totally different, right? If we count the days, we've already been here for about three months. So, technically, tomorrow should be her birthday. So… what should I do?"
Selena sighed softly in his mind. "Are you asking what gift to give her, or whether to celebrate it now or on the real date?"
"Both, actually," Akira admitted.
Selena sighed softly. "You used to give her teddy bears and cute stuff, remember? Why not do that again?"
Akira frowned. "But she's in high school now, right? Isn't that kind of… childish? Shouldn't I get her something more mature?"
"I don't think she'd mind," Selena said thoughtfully. "But fine, what do you think would be a good gift then?"
Akira groaned softly. "I don't know! You're a girl, what do you think girls your age would want?"
"Hmm…" Selena hummed. "Maybe jewelry?"
Akira sighed. "Jewelry from this era is way too old-fashioned. And I can't make anything modern without using magic."
"Can't you make one by hand?" Selena suggested innocently.
"Not without magic," Akira muttered. "And the tools here are ancient. I don't even know how to make something like that normally."
Selena chuckled teasingly. "Then how about clothes?"
Akira groaned again. "Same problem. Things here are old-fashioned, and I could make them, but as you know, my style is a bit out there?"
Selena paused before teasing, in a sweetly mischievous voice. "Then why not gift-wrap yourself and say, 'The present is me'? That'll get a reaction."
Akira stared blankly at the ceiling. "I have a feeling I'll die if I do that."
"Then I'm out of ideas," Selena said playfully. "Wasn't there an episode in the anime about her birthday? What gift did she get then?"
"I think it was cake… but I'm not sure if that version of her even applies. She feels a lot different from the anime counterpart," Akira said thoughtfully.
Selena hummed. "Of course she is. In her original world, Erika had a lonely childhood; her mother pressured her to find a servant. But you being here changed that. You became her friend and… well, started doing your little 'Phineas and Ferb' adventures with her, all your childhood."
Akira smirked. "I always wanted to do those, and she made the perfect girl across the street part." He paused. "By the way, what about her mother? I only met her a few times, and for some reason, it felt like she really doesn't like me for some reason."
Selena chuckled. "Her personality's different in this world, too. And I don't think she's forcing Erika like her anime counterpart. As for why she dislikes you… Well, that's entering spoiler territory."
"Whatever," Akira said, waving it off mentally. "If she ever tries to force Erika into something, she'll have to go through me first."
"Don't worry," Selena said softly. "A lot of things have changed. I doubt she's like her anime version anymore. A lot of things have changed in this world. And a lot of characters act differently from their original versions. Some of it's because of this world's nature, and some… because of you."
Akira blinked. "Because of me? Like who?"
"For example, Rias Gremory," Selena said casually. "You spent a whole year with her, and she's changed a lot because of you."
"Huh? I don't think she's that different from her anime version," Akira said skeptically.
Selena laughed. "Oh, she's different all right. You turned her into an otaku just like you, brother."
Akira's eyes widened. "That's not true! She already liked that stuff!"
"Not like this," Selena teased. "In the anime and light novel, sure, she was interested in human culture in general, but now she's completely addicted to anime, thanks to you. You've turned her into a full-blown fan."
Akira groaned. "I just wanted to spread the greatness of anime, that's all."
"Well, mission accomplished," Selena said with a grin in her voice. "And she's not the only one you've converted. You even turned that other girl into an otaku, too."
Akira blinked, realizing who she meant. "Wait, that girl was already supposed to become an otaku! I didn't change anything!"
"She was supposed to like cutesy, childish things," Selena replied slyly, "but now she's obsessed with action stuff too. You definitely made it worse."
Akira sighed in defeat. "I swear, I just wanted to share the love of anime. Anyway, back to Erika. Help me figure this out first."
"Alright, alright," Selena said, amused. "But are you even sure she wants to celebrate tomorrow? Actually… wait, it's already past midnight, isn't it? So technically, it's today."
Akira blinked. "Oh. Yeah, I guess it is."
"Then the best thing to do," Selena suggested, "is to just ask her yourself."
Akira sighed. "Yeah, maybe that's the best way."
He sat up on the bed, stretching slightly.
"Wait," Selena said quickly, "you're not seriously going to ask her now, are you?"
"Yeah," Akira replied casually. "Why not? I can also wish her happy birthday, right?"
There was a brief silence. Then Selena's voice came through again, playful but cautious. "…That's not a bad idea, actually. But if you're going to do it, make it a surprise."
Akira smirked. "Got it."
Akira stood up and quietly walked to Erika's bed. She was fast asleep, her golden hair softly glowing under the moonlight.
Erika, who had been fast asleep, suddenly felt someone whisper her name.
"Erika… Erika…"
A gentle shake followed, pulling her from her dreams. Her eyelids fluttered open, only for her vision to be filled with Akira's face, way too close to hers.
"Happy birthday," he said softly, smiling.
For a moment, her half-awake brain didn't process it. Then.
CRASH!
A startled scream echoed through the house, followed by the unmistakable sound of something or someone slamming into a wall.
Everyone stirred awake, but upon realizing it came from Akira's room, they all sighed and went back to sleep, clearly used to their antics by now.
Back in the room, Akira sat in seiza, a deep red mark swelling across his cheek. It was already beginning to heal, his regeneration kicking in, but that didn't make it hurt any less. Across from him stood Erika, hair messy from sleep, her pajamas slightly rumpled, and her expression radiating pure disbelief mixed with irritation.
"What in the world is wrong with you?" she asked flatly, arms crossed.
"I just wanted to surprise you a bit…" he muttered weakly.
"That's not how you wake someone up, especially a girl," she snapped.
Akira bowed his head slightly. "I'm sorry…" he mumbled, looking genuinely regretful.
Erika let out a long sigh. Somehow, no matter how much he annoyed her, she could never stay mad for long. She wondered why.
Then, deciding she wasn't done, she looked upward and said aloud, "Selena, why didn't you stop him?"
Selena's cheerful voice echoed telepathically in both their heads. "Well… I thought it would be more fun that way! Teehee~"
Erika's eyebrow twitched. "So it's your fault then."
Akira turned his head sharply. "Sister, how could you!?"
"Hey, I didn't make you do it," Selena replied. "I just didn't stop it, so technically, it's not my fault."
Akira pointed accusingly at the air. "But you told me to go for it! You even said to make it a surprise!"
"I was just encouraging your enthusiasm!" Selena countered playfully. "It's still your fault!"
Akira sighed dramatically. "Just you wait, sister. Mark my words, vengeance will be mine."
Erika rubbed her temple. "Honestly…" before saying aloud, "Just get up and tell me why you woke me up in the middle of the night."
Akira stood, brushing off imaginary dust from his clothes. "Well, the thing is… today's your birthday. In a way."
Erika blinked. "What do you mean by 'in a way'? My birthday's on June 7th."
"Yeah, but the time difference between our world and this one is different," Akira explained seriously. "If you count the number of days we've been here, that means today would technically be your birthday."
Erika stared at him blankly. "That's… confusing. So what will you do when the actual June 7th comes around here?"
"Maybe celebrate again?" Akira offered innocently.
"That's not how birthdays work." She folded her arms. "Besides, I don't really celebrate mine anyway."
"Huh?" Akira blinked. "We always celebrated your birthday."
"Yeah," Erika said quietly. "But after you left, I stopped. My mother and brother aren't the type to celebrate it."
Erika looked away slightly. "Yeah, but after you left, I stopped. My mother and brother… they're not really the type to celebrate things like that."
The truth was, for dhampirs like her, or vampires in general, they have a really long lifespan, so long that birthdays held little meaning. But when they were children, Akira always insisted on celebrating hers. He would rope his family and Iori in and have a big celebration, and he even baked cakes for her. But after he and his family left Japan, she stopped celebrating entirely. Her brother had offered once or twice, but she refused to do it; she was too upset back then to enjoy it without Akira.
"I still sent you gifts, though," Akira said proudly.
Erika tilted her head. "What gifts? We didn't have any contact for years…"
Then her eyes widened. "Wait… those auroras… that was you!?"
Every year on her birthday, a beautiful bluish-purple aurora would appear across the night sky. She'd always thought it was just a coincidence, a strange natural phenomenon.
Akira smiled faintly. "Yeah. I couldn't send you anything directly, so I improvised. I fired my spells into the upper atmosphere, and they will travel through the space and form an aurora over Japan. My parents never noticed, since I just launched it into space."
Erika stared at him, mouth slightly open. "Are you nuts? Do you know how much trouble that caused?"
It had caused a commotion. Every year, scientists and meteorologists went wild trying to explain the mysterious "Aurora," which appeared despite all logic. Some even theorized it was an alien event.
Selena joined the conversation with a teasing laugh. "Actually, our parents knew what he was doing. They just decided to turn a blind eye to it."
Erika blinked. "Wait, seriously? Then how did I not notice…?"
She trailed off, realization dawning on her. Every time those auroras appeared, she had been too busy suppressing her loneliness, too convinced that Akira was gone for good. She'd never even considered the idea that he was behind it.
Now that she knew, a warm feeling bloomed in her chest.
Blushing slightly, she smiled and whispered, "...Thank you."
Akira smiled faintly. "Don't worry about it." Then, after a moment of silence, he added, "But… what should we do about this birthday? I can't exactly use magic here."
Erika tilted her head thoughtfully. The whole different world–different timeline thing was confusing even for her. She sighed. "Honestly, this is complicated. The time flow here and in our world doesn't even match, so how would birthdays even work?"
After thinking for a while, she looked at him and suggested, "How about this, let's only celebrate our birthdays when we're back in our own world, and count our age based on that time?"
Akira blinked. "Huh? How would that work?"
Erika pointed at herself. "Well, if you look at my brother and my mother, I don't think I'm going to age any more than this." She paused, then tilted her head curiously. "Wait… how do you guys even age?"
Before Akira could answer, Selena's cheerful voice echoed telepathically in both their minds. "I don't think we'll age much either. Remember our parents? They still look like teenagers."
Erika chuckled softly. "Yeah, that's true. When you and your parents walk around in public, most people probably think you're all siblings."
Akira smirked. "Hey, at least I look younger than my parents."
Erika sighed with a half-smile. "Yeah, that's true". Thinking how her mother looks like a middle schooler… or even younger.
"Wait, that's not the point," she said, waving her hand. "So, we both basically don't age past this point. Why don't we just celebrate and count our ages by our home world's calendar?"
Akira thought for a moment, then nodded. "Yeah, that works for me. But what about days like this one?"
Erika smiled lightly. "Hmm… we could just make it a casual celebration. Eat something nice, relax, and have fun. No formal stuff."
"Sounds good to me," Akira said. Then he looked off thoughtfully. "But I wonder how long I'll stay sixteen if we go by that logic. I didn't age past sixteen even in my previous life."
Selena giggled telepathically. "It might take a few years, but you'll become seventeen one day, brother."
Akira groaned. "Yeah, that's not helping."
A few hours later or perhaps the next day, Akira decided to do something anyway. He spent most of the morning in the kitchen, crafting a massive, beautifully decorated cake entirely by hand. Despite not using magic, it turned out surprisingly perfect.
That evening, he presented it to Erika.
She smiled softly, genuinely touched, and they shared the cake with everyone, though, of course, only Shinobu could eat, as demons couldn't handle human food.
It wasn't an extravagant celebration, but for Erika, it was more than enough.