(loved trope) Two characters are extremely similar, and hate each other for it.
Athena and Odysseus - Epic the Musical
Athena and Ody are both genius strategists with incredible fighting ability on top. They're also incredibly prideful, vain, and flawed individuals that butt heads right up until My Goodbye.
Megamind and Tighten - Megamind
Megamind wanted a hero to challenge his superior intellect, so he gave Metroman's DNA to an arrogant manchild. Hal's new power brings him into a downward spiral, ultimately leading to Megamind becoming the hero that Tighten was always intended to be.
Dr Robotnik and Starline - Sonic IDW
When the egomaniac who wants to take over the world thinks that you're too ambitious and need to be taken down a peg, you've made a grave error.
Hunter and Cal - Unmatched: Rising Legend
Hunter and Cal are both highly intelligent, capable people. They're also deeply selfish people, with Hunter paralyzed by his own grief and Cal descending into chaos as a result of his abusive father. In book 2 of the web novel series, Hunter realizes that he shares the same fundamental flaw as Cal, and if he doesn't change, he's going to get everyone he loves killed.