Non sex related stuff is great too! And I love asks about my OCs, even indirectly!

Dzamie is the obvious choice, since he would be successful, and his aptitude at pyromancy makes him a good fit for the fiery Virus 'mons. However, he's not great at teaching people how to improve, themselves, and he has trouble focusing attention on others, which is an important skill for any trainer.

HM would also be successful at getting them stronger, but at best their personalities would clash too much to keep it up and at worst HM would corrupt them.

...y'know what? It's pretty out of left field (I don't talk about her much, either), but Mai the succubus is probably the best option. She's a teacher, herself, and while her usual subject is mathematics, she's no liability in a fight and could probably adapt well enough.