Basically One Punch Man but shoujo reincarnation version.
MC had a short life, always sickly and on death's door. When she gets reincarnated as the supposed final boss, the sheer joy and limitless possibilities of having a healthy body prevent her from having this destined tragic childhood. Like, her first life was already on nightmare-mode and now that she got a good body starting from light to mid difficulty everything's a breeze. All the lil twists are well-explained by the now constantly mentally exhausted cat familiar who watches over MC, but it's less about being worried for her and more about how fucking far the intended storyline is going to drift this time. The whole thing is just taking the piss in the best way, love it.
Nengan no Akuyaku Reijou