After a fierce battle against the demon Heisuke, Goku fell asleep inside Fumiko's house, a girl he met in the village. As the day unfolded, Goku woke up, rubbing his eyes and yawning. As he looked at his body, he noticed he still had some injuries, though they weren't severe.
"Good morning, Goku," said Fumiko, who woke up before him.
"Good morning, Fumiko," said Goku, standing up and grabbing his katana,"today I'm gonna leave and continue my journey..."
"I see..." whispered Fumiko, "thank you for last night, you saved us..."
"No problem. That's what a demon slayer does," replied Goku, "I hope I'll see you again, Fumiko. Bye..."
Goku got outside the house and started walking outside the village.
"Goodbye, Goku... May your path be safe..." said Fumiko, ensuring he couldn't hear her.
As Goku continued his journey, he started looking for a doctor to heal his few wounds from. After several minutes of searching, he reached another village. Here, Goku found a hospital.
"I hope I'll find someone useful here..." he whispered. Goku knocked at the door twice, and a woman with violet eyes, a white haori with flowers on it and black hair gathered in a tie.
"Hello, demon slayer. What do you need?" She asked.
"Are you a doctor?" Asked Goku, "if so, can you heal my wounds?"
"Yes, I am a doctor," said the woman, allowing him to enter, "come inside, I'll heal you."
As Goku entered, he saw another young boy, with green hair, violet eyes and a hateful grin.
"Who the hell are you?" He asked.
"A demon slayer," replied Goku.
"Why are you here?" Asked the guy.
"Quit bothering our guest, Yushiro," said the woman. Yushiro shutted up.
"So... What's your name?" Goku asked.
"My name is Tamayo," she replied, "He's Yushiro."
"Why does he smell like a demon?" Demanded Goku.
"Because he is one," said Tamayo, "he's the only demon I managed to create in all my life."
"What about you, slayer? What's your name?"
"My name is Goku," replied the boy, "just Goku. No surname, from what I know."
When Tamayo heard that name, her heart stopped for a second. Goku... Could it be that Goku? She one she raised for five-hundred years?
"What... what did you say your name is?" She asked again.
"Goku..." Goku said again. In that moment, realizing Goku was really that Goku, Tamayo's eyes welled up with tears, and without hesitating, she hugged him tight, as if she just found a lost child.
"Is it... Is it really you... Goku...?" She said, still trying to process.
"Uhm... Excuse me, Tamayo-san, but I don't get it... Why are you hugging me?" Asked Goku.
"I'm so happy you came back to me..." She said again, apparently ignoring Goku, but still hugging him. Then, she broke the hug.
"Now I'll explain you everything... Please, sit down.." she said, her voice still broke from crying. As Goku sat down, Tamayo and Yushiro did the same.
"I knew you'd become a slayer... But I'd never thought you to come back to me..." said Tamayo.
"Can you explain better?" asked Goku.
"Sure..." said Tamayo, "Goku, you... Are a hybrid. Half demon, half human."
Goku's eyes widened.
"W-what?" He said, in disbelief, "half demon? Since when?"
"Since your birth," replied Tamayo, "earlier, you said you don't have a surname. But you do. Your surname, Goku, is Tsugikuni."
"Tsugikuni? Isn't it the same surname of the legendary Yoriichi, the one who created Sun Breathing?" asked Goku.
"Exactly, Goku. In fact, you are his son," said Tamayo.
Goku's eyes widened once again, even larger this time.
"I... I am Yoriichi's son?" He repeated, "and also, half demon? Is this a joke?"
"Nope. Everything's true, Goku," said Tamayo.
"But if this really is true... Why do I find out only now?" Asked Goku.
"Because your true identity would have killed you," said Tamayo. Then, she started explained.
"Five-hundred years ago, your father faced Muzan and nearly killed him. Then, he freed me from his control. That's why I can say his name. Neither me, Yushiro, nor you are related to him. One day, your father came to me, asking to me to take care of you for centuries after his death. To ensure you'd live forever, he injected in you demon cells, which turned you into a hybrid. You're immune to sunlight and have infinite lifespan, but you do not have regeneration or unlimited energy, unfortunately. For five-hundred years, I kept you as a baby for all that time. Then, when I abandoned you, you grew up normally. So you're physically nineteen, but biologically five-hundred and twenty-five years old. Also, just like your father, you're born with a Demon Slayer Mark, but you can't use it yet. That's all."
When Tamayo finished the explanation, Goku was in disbelief. All those informations... were a lot o take in.
"You know what? I may believe you, but my katana doesn't," said the boy, standing up, "until I have proofs I'm really Yoriichi's son, I won't believe this. But... I do believe in the hybrid and mark things..."
Then, Goku got outside the house, with his katana in hand.
(If I'm really his son... Then I should be able to use Sun Breathing...) he supposed. Then, with a movement of his sword, Goku said:
"Sun Breathing: First Form -- Dance." And unexpectedly, from Goku's katana emerged crimson flames.
"It's true... I'm really a Tsugikuni..." he realized.
"Do you believe now?" asked Tamayo, who reached him.
"I do now," said Goku.
One month passed. In this month, Goku trained under Tamayo's wing, in order to learn Sun Breathing and improve Flame Breathing. He knew: Now that he knows his true identity, he has to hide it.
In this month, Goku learned four out of the thirteen forms of the Sun Breathing: The first, the second, the fifth and the eighth. As for the Flame Brething, he could use five out of the six forms.
After this month, Goku was ready to continue his journey.
"So... you're leaving?" Asked Tamayo.
"Yes," replied Goku, "thanks for taking care of me for five-hundred years... Okasan."
Tamayo's eyes widened, and she hugged Goku.
"I love it when you call me 'okasan'..." she said.
"I know you're not my biological mother, but..." said Goku, hugging her back, "for me, it's like you are."
"Okay, okay, enough hugging," said Yushiro, irritated, "don't get too close to Tamayo-san, Tsugikuni..."
"Come on, don't be jealous, Yushiro," said Goku. Yushiro snorted.
"Try not to die, Tsugikuni. Tamayo-san would be sad," he said.
"I won't," said Goku, "Well, time for me to go."
But then, before he could leave, Tamayo asked him one more question.
"Goku, how will you hide your identity?"
Goku stopped for a bit, then replied.
"I will walk under the alias of Goku Urokodaki, in honor of my master Sakonji. As for the Breathing Style, I'll keep Sun Breathing hid, and I'll keep using Flame Breathing. That's how," he explained.
"I see..." whispered Tamayo, "take care, my son..."
Goku nodded, and then turned back, walking and disappearing inside the forest.
Chapter 4 - End.