Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 3 - 3-2. Master of the Beastkin Girls

Ron finds himself reborn in the world of One Piece, stranded on a remote island in the East Blue. But he's not just any ordinary child—he’s bonded to a mysterious sign-in system that grants him powers with every new location he visits.At his first sign-in, he unlocks the legendary Sun Breathing Technique, along with a boost to his vitality. From Shitmotsuki Village to Skypiea, Enies Lobby to Marineford, Ron travels the world, collecting extraordinary rewards that make him a force to be reckoned with. The Raikiri, one of the 21 Great Grade Swords, Armament Haki, Observation Haki, and more fall into his hands.As Ron steps onto the battlefield of Marineford during the legendary Summit War, the mightiest warriors—Four Emperors and Marine Admirals alike—pause, stunned by his presence. But Ron merely waves them off, “Don’t mind me. I’m just passing through.”Join Ron on his journey across the Grand Line as he signs in at iconic locations, growing stronger with every step. This is not just an adventure—it’s a legend in the making.

I had to take him home and raise him. There was no bathtub or a large basin at home, so I had to put him in the washing machine for the time being.

It was an hour later before I remembered it again, by which he had been washed extremely clean.

- Description from Novelupdates

So here's the pitch: I got reincarnated with Mangekyo Sharingan.Sounds overpowered, right? Instant win button?Except I can barely keep it active for thirty seconds without feeling like my brain's being microwaved. My chakra reserves are pathetic. My combat experience is zero. And the system that gave me these powers took one look at my situation and said “good luck” before fucking off into hibernation.Oh, and the Hero Killer—the guy who murders heroes for not being “worthy”—just decided my mom wasn't good enough. She'll never walk again.I know when he'll strike next. I know where. I've got exactly four weeks to train.Four weeks to go from “can't throw a punch without tripping” to “can survive a fight with a serial killer.”The smart move? Stay out of it. Let the pro heroes handle it.But I'm fifteen, angry, and apparently making life decisions with the wisdom of a shounen protagonist.At least I'm in General Studies. Low expectations.What does being a hero have to do with revenge anyway?

“Ding! Choose your idle skill.”“Ding! Idle complete. Language level +999.”“Ding! Choose your idle skill.”“Ding! Idle complete. Basketball level +999.”After a freak accident, Qi Ning acquires the “”Unlimited Idle”” system. But just as the system binds to him, it crashes, leaving a repair time of 999 years. However, to Qi Ning’s surprise, the system still allows him to idle, and with every second of idling, any chosen skill instantly reaches level 999.With his life now dramatically transformed, will Qi Ning’s rise from mediocrity be unstoppable?