Regina started out as a gijinka of a Gyarados I had in Pokemon Pearl. I'd never actually invested in training a Gyarados beyond just evolving a Magikarp for the Pokedex entry. But this time I was like "NO, I'm gonna do it this time. I've never trained one for real before, but THIS IS THE TIME." So I got this little girl Magikarp and was super adamant about her beating every foe she came across no matter what, regardless of how weak her attacks were before evolving. In particular, I was super stubborn about making her defeat all the Pokemon from one of the early gym leaders and just loading her up with Potion after Potion, refusing to switch her out or let her faint until she beat everyone. XD And now she's such a beast as a Gyarados, even though from a realistic point of view, none of that actually mattered in how tough she'd be.
At some point I decided to draw all my Pokemon as humanoids just for fun, and I eventually made them all into actual characters for my main stories. Regina works as a bouncer at a bar, which she towers over because she's monsterously tall. ^^; I just figured a sea monster lady as a bouncer would be a fun thing to do, and she's as ferocious in character as she was in game.