I Only Have One Skill Slot

Arc used his fully mastered skill as a payment to the dungeon trader while he was nearing death after defeating the Calamity ranked boss monster.
His eyes were fuzzy as he could not see clearly but he knew that this deal will not be bad because fully maxed skill is rare to see among divers.
This deal brought Arc to the past when game named ‘Ultimate survivor’ was turning in reality.
But this deal was not good for him because his skill slots were limited to only one, which was a huge no no in this dangerous world.
But was there any benefit to that deal as well apart from bringing him in past.
Well, can he save the family that he had once lost before or is he still powerless boy that can’t stand against his own problems by himself.