I've had the idea for Battlesquad High in the back of my head for a few years now, since at least 2005. The spark came from finding an obscure Japanese game, Princess Maker 2, on Home of the Underdogs.
I don't recall if I found it before or after picking up the first Sims game, but there's something about time management and stat progression that absolutely grips me. Deciding between increasing strength and getting paid by working on a farm versus going to school and increasing knowledge and refinement, for some reason, is my idea of fun.
I've also always been a fan of turn-based strategy games like Final Fantasy Tactics, Front Mission, and Disgaea. Guiding individual units through a string of battles, raising their stats, buying them better weapons, seeing their performance improve in battle. You almost get attached.
Toss in a love for the battle school concept from Ender's Game and a steady diet of anime before I even knew what anime was and Battlesquad High was the inevitable result.
You guide a team of mech pilots through a season of competition against other schools. You can befriend the brains in the engineer corps to help R&D new mods for your mechs, as well as people from the officer school to lead and give advantages to your pilots.
I'm getting a little ahead of myself, though, as my first project will focus on establishing the universe and some of the characters. I'm going to do that through the medium of Visual Novel and add gameplay concepts from there. There are already a few "sim" type VN's (Princess Maker 2 was a raise-your-daughter sim) made using the Ren'Py engine so it's a good choice for me, and I have a little experience with the Python programming language.
So teens in outerspace, making friends, dating, designing and piloting robots. Sounds perfect!