I love Eggman x Tails tailsegg/eggtails because they're so alike in minds and genius but also so different because of good and evil, young and old. The compare and contrast is so hot. Eggman being a dirty old man taking advantage of and tainting "young Prower's keen mind" and potential, as he puts it in the Egg Memos.
The way in the SA2 journal recap he says "killing you will be my pleasure" to Tails and the in game line that immediately follows it "you're just a kid, you couldn't beat me in a hundred years!" That is a big old sadistic pervert. The human being the predator and fox being the prey is a great table turn.
Eggman recognizes Tails is a worthy rival but his pride won't let him admit it much and he's too selfish and still feels like he's above him for just being a kid. But he really wants to win and feel superior and his ways of having power get more sick and twisted over time. It's set up perfectly for Eggman to manipulate and prey on him.
If Eggman could get his hands on Tails and steal him away from Sonic, he'd have fun playing around with him, using him and his intelligent mind for his plans, and grooming him into believing he's the only one who truly recognizes and appreciates his skill. His tight little cub butt is irresistible to him and he ends up taking him by surprise and raping him. After that, he's hooked on training Tails to be his cute little fuck toy whether he likes it or not. <3