The Villainess, Cecilia Silvy, Doesn't Want to Die, so She Decided to Crossdress - Volume 1, Extra: Gilbert’s melancholy

A boy from 21st century Earth, met an accident and later was reborn in Naruto’s Ninja World.
He is born in Uchiha Family and becomes the useless brother of Itachi Uchiha and Sasuke Uchiha…. Let’s see how he changed the Naruto world.

- Description from Novelupdates

In the last life, Lin Yu Tong chose to fly with Shen Jun for his own happiness, whereby he ended up creating an irreparable regret for a lifetime. However, such a contribution has not been able to exchange the happiness of a lifetime. Shen was derailed and Lin Yu Tong had an accident.

In a world of brooding heroes and dark justice, one mercenary stands out—not for his skill, but for his relentless sarcasm and love for chaos. A self-proclaimed anti-hero, he finds himself working with the Titans, much to their frustration. While undeniably skilled in combat and nearly impossible to kill, his real talent lies in driving his teammates insane with endless jokes, fourth-wall breaks, and questionable decision-making. Whether it’s swapping Robin’s gadgets with toy versions, turning serious battles into slapstick comedy, or giving monologues mid-fight, he thrives on pushing everyone’s patience. But beneath the humor, there’s a sharp mind, a tragic past, and a surprising willingness to do what others can’t. While the Titans may roll their eyes at him, they also know that when things get truly dire, he’s the wildcard they need. Love him or hate him—he’s here to stay, and he’s having way too much fun.