After a person dies and turns into a ghost, it's because they have unfulfilled obsessions from life, obsessions so deep-rooted and important that they persist after death, manifesting as a soul.
Ash can indeed directly purify the other party using Aura Power, but if he can resolve their obsession before purification, it might benefit their reincarnation.
This is something the experts in the group have mentioned. Like Aura Ash, who has encountered a ghost before, it was a young boy. After resolving his obsession, the boy ascended peacefully.
Moreover, he could feel a mysterious power attached to him, an intangible force that made his journey smoother and accelerated his strength enhancement.
Perhaps such a thing might be akin to merit.
And now, under Ash's persuasion, the ghost girl's beautiful eyes showed gratitude and relief. She nodded towards Ash, lightly smiling and saying, "Thank you, young man. I hope Gastly can help you, and I hope you will treat Gastly as you promised."
"Don't worry, I will." Ash solemnly nodded, then held his hand out towards the girl with Aura Power surging from it.
Under the influence of Aura Power, the ghost girl was rapidly being purified, and her somewhat deteriorated soul also became purer along with the purification of Aura Power.
During the purification, the girl's face revealed expressions of relief, tranquility, and gratitude.
Because a wisp of obsession had kept her in this world till now, and since Gastly had found a good home, she no longer needed to worry about Gastly. Now, she could finally go find her lover from back then.
In a moment, the girl's ghost was completely purified, and Ash felt the mysterious thing Aura Ash mentioned, something intangible seemed to cling to him. Although his body felt no different, his mind seemed to become more lucid.
After purifying the girl, Ash looked at Gastly, who had reverted to his original form, and silently placed a Pokeball in front of him.
"Keep your promise, Gastly."
"Don't worry, don't worry. I said I'd become your Pokemon, and I will. I never thought after being free for thousands of years, I'd become a Trainer's Pokemon one day." Gastly sighed, then transformed a hand to touch the Pokeball in Ash's hand.
As he transformed into a light and entered the Pokeball, it clicked, signifying Ash's successful capture of Gastly.
"I caught Gastly!!"
"Pikachu!"
"Laru~~"
After capturing Gastly, the two little ones customarily celebrated for Ash, but at this moment, an unexpected change occurred as Ralts's body burst into a brilliant light!
Ash was stunned for a moment and then instantly realized that Ralts was about to evolve!!
Ralts had long been on the verge of evolution but had been in a conflicted state, torn between gaining stronger power through evolution and not being able anymore to sit on Ash's shoulder like before.
If Ralts was a little girl, then Kirlia would be a maiden. As a maiden, she naturally couldn't do the same things as a child.
But no matter what, she had to grow. Although today dealing with Gastly she had a Foresight that helped Ash, it wasn't much different from doing nothing.
If she could become a Kirlia or even a Gardevoir, perhaps she could be more helpful in such a battle.
Thus, Ralts decided to evolve now!
As the dazzling light slowly faded, Ralts's appearance also changed dramatically.
The once small stature suddenly grew to reach Ash's waist, and her light blue hair became much longer.
However, given her growth in size, the lengthened hair didn't obscure her eyes more. A pointed fringe in the middle, the hair extended down the sides of her head toward her neck.
Her orange beautiful eyes twinkled in the night like two stars.
Her originally slightly pink body turned into a flawless white, with her arms and legs growing more slender. At first glance, she might even be mistaken for a teenage human girl.
"Kirlia, you've evolved!" Ash was delighted to see Kirlia's evolution.
Ralts had already been on the verge of evolution for some time but delayed the process. If Ralts's Ability Value hadn't been steadily increasing, Ash might have suspected something was wrong with Ralts.
At the Ordinary Peak, Ralts had pushed all her Ability Value to S level, and now after evolving, her level leaped to Advanced Intermediate, while her Ability Value decreased to A.
Generally speaking, advancing two minor levels should have reduced Ralts's Ability Value more, but because Ralts's initial Ability Value was S level, it only dropped to A level.
With Kirlia's current strength, she's a standout among the Advanced Level.
Capturing Gastly and evolving Ralts made today a doubly joyous occasion; Ash was overjoyed.