It was quite a while ago, but yeah, I'm pretty sure I spent several weeks on it. (Maybe months.) I get obsessive when I'm on a creative project.
When I used to have the original version of Apeiron, I always played it with a Star Wars mod someone had uploaded. When they made Apeiron X, the old mod no longer worked, and I decided it had to be recreated for the new version. Figuring out how to change the graphics was not much trouble once I learned to open the resource files, but the sound effects were a hassle. The people from Ambrosia said they had no record of which sound effect was for what action, and they were in some weird sound format that would only play in the game, so I had to install sounds one at a time and play the game to see when they turned up. There are still a few sound effects I have no clue about the triggers for. (When Excel yells, "Let's go for it!" it seems to be random. In the Star Wars version, I used Ben Kenobi saying, "Use the Force, Luke!" or something like that.)
Anyway, once I had learned everything making the Star Wars mod, and uploaded a Guide to Modding Apeiron with my file listing, I wanted to make another one, and Excel was the one among my favorite anime with the most perfect scenario. It's the only way I play Apeiron any more-- somehow it's just so much more fun than either the original or the Star Wars.
Excel was much more complicated to make, too--I modified almost every single graphic, and animated them. Star wars used a lot of the original game graphics, and the TIE fighters and other ships needed very little animation.
Kudos to Ambrosia for making such a tweakable game. Adding the afro to the caterpillar in the end animation was sort of an "OMG I can't believe I can do that!" thing.
