Felix is the first and oldest, created pretty much on a whim. The classic self insert OC, the only really unique feature is the whole "transistorized brain in a body made of printed microbots" thing, which lets him look organic without being organic.
Blunt was designed specifically to be robust, capable, and fun. He occupies a sweet spot where he's large enough to move heavy things around and has wings big enough to actually fly, but he can still fit inside and use most "normal" infrastructure.
For Toste, well- I was watching somebody else's demoness OC ~~cook a hotdog with their lady parts~~ and my brain instinctively said "I could do WAY better than that with a nuclear reactor". So I then set about figuring out how small you can feasibly make a nuclear power plant that actually goes critical (an RTG is NOT enough), and shoved that into a body that could handle the waste heat, put the power made to use, and look good doing it.
