Is this a sequel?

what does all different variations of metal pieces do, went from stainless steel to titanium, godium etc. what do they do? how do i use them, i went through the game collecting countless pieces without knowing what they are for or have interacted with them in any significant way....

They are really strong and seem to almost oneshot me no matter how strong i get.

It's possible to win the tournament and pay back your debt on the first run. You don't have to play it twice. You just need to consistently improve your mech and skills to a sufficient level. Final fights are difficult though. You gotta be ready for them. If you feel that reaching investigation level 40 is easy, you should stand a chance. In case you fail on the first run, you can try again in New Game+ - keeping parts equipped on your mech, experience stats and some other minor stuff. After paying back ...

Like, do I have a limited amount of ingame time/missions to pay off the debt or it's game over?