Isaiah was created out of providing a sorta, voice of reason to Simone. He's a very sarcastic and handsome little mouse.
Humorously, one detail about his character design, is I wanted to embody a handsome mature adult character in a small stature. If, he was the average human height, he'd be seen as a mature dommy type character. Its his size that makes him cute. The more I draw him the more I'll try to protray him as the cool type character.
Oh, and yeah, thats Kaitee in a swimsuit, ealry design. He doesn't wear that particular suit in the comic.