A mentor figure could be the one betraying the mc. The mc trusted this mentor completely, but the mentor has some hidden motives. Maybe they are working for a greater evil and see the mc as a threat or a tool to be used, so they betray the mc, which then causes the mc to turn dark.
Well, often in such a 'ash gets betrayed fanfiction', the story might start with a seemingly normal day for Ash. Then, out of the blue, someone he trusts deeply, like Pikachu or one of his human friends, does something that he perceives as a betrayal. This could be something as simple as not believing in him during a crucial battle or siding with an enemy for a reason that's not clear to Ash at first. It can create a lot of emotional turmoil for Ash and make for a very engaging read.
The mc ride manga and anime are related, but the anime can make changes to enhance the viewing experience. Sometimes characters' expressions or actions might be emphasized differently.
One great anime is 'Sword Art Online'. The main character, Kirito, is extremely overpowered (OP). He is highly skilled in the virtual reality world of SAO. In the series, he also has a love story with Asuna. Their relationship develops as they face various challenges together in the dangerous game world.
One possible reason for Ash getting betrayed in the fanfiction could be misinformation. A villain might spread false rumors about Ash, making his friends believe he has done something wrong. His friends, without verifying the truth, turn against him. It's a sad situation where lack of communication and trust plays a big role.
At first, he's likely to be shocked. Issei is often portrayed as a character who trusts easily, so betrayal would come as a big surprise. He might not believe it at first and try to find reasons to justify the actions of the person who betrayed him.
One possible plot could be that the main character (mc) is betrayed by a close friend or ally. This betrayal shatters their trust and makes them see the world in a different, darker light. They might then start to use more ruthless methods to achieve their goals, perhaps seeking revenge against those who wronged them.
There were many anime works where the male protagonist got angry and turned into an awakened character.
Naruto Uzumaki in Naruto: When threatened or challenged, Naruto will show strong willpower and anger, transforming into a Nine-Tailed Fox to achieve his powerful goal.
Fliesa in Dragon Ball: As a cosmic pirate, Fliesa has super strength. When he feels angry, he will transform into a "Fliesa Lion" to show unparalleled strength.
3. Monchi D. Luffy in One Piece: When threatened or challenged, Luffy will show strong willpower and anger, transforming into a rubber man to obtain more powerful abilities.
4. Shizuka Juushirou in Gintama: Shizuka Juushirou is a ronin. When he feels angry or dissatisfied, he will transform from an ordinary ronin into a "ghost cut" and become a powerful warrior.
The transformation and awakening of these characters were based on their anger and challenge, thus revealing more powerful abilities and strength.
One good anime is 'Sword Art Online'. The main character, Kirito, is extremely overpowered. He's highly skilled in combat within the virtual world of SAO. And there's a love story between him and Asuna. Their relationship develops as they face various challenges in the game world.