Each girl has their own ending, the only thing that changes is that you get the h-scenes of the girl you want and a couple of events, the rest honestly is pretty much the same thing, so unless you want 100% of the game I don't suggest you do all endings. Excluding Senna and Kunagi, you can get all the other 4 heroines regardless of the route, to get each ending just get the heroin's love up to 8.
Just like redeclipse said hardmode unlocked by going to the roof after beating the game once, chaos mode same thing except you need to clear hard mode before unlocking it.
Turns are 24 school, 24 district, 99 national.