There shouldn't be and mustn't be such content. Pokemon is a beloved franchise for all ages, and pornographic comics related to it are completely unacceptable and against all norms of decency.
Pokemon porn comic is neither legal nor ethical. It's a form of content that is considered offensive and against the law. Such material can cause harm and has no place in a civilized society.
Pikachu is a very likely candidate. It's Ash's most iconic Pokemon and has a deep bond with him. Whenever Ash is in trouble, Pikachu often steps up to protect him.
Porn comics tend to have a narrow focus on sexual content, with little emphasis on character development or plot. They may also violate moral and legal standards in many places.