Ok, it not that complicated.

First you need your gf's to learn there abilities, like str, and vit and all the things so you can use them to your advantage.

Ok, when the things on your junction screen are white, you can use them. What you do is go junction, magic, then you just put the magic in the slots. Diff magics put diff amounts of the stat to go up. For example, putting 100 ultimas to a slot will make it go much higher than putting 100 fires. You just mix and match to your liking. I can give you the best magics to junction to each stat if you want but i am to lazy right now.

In this way you can raise your hp, also by putting on abilities such as hp+*80% or something like that on your auot abilities screen. Try not to level up, and learn how to use the junction to attain all your power.