Naruto: I Give You a Life-for-Life System, and You Spend Other People's Lives

[System + transmigration + decisive killing + invincible protagonist + no heroine + no fawning over Konoha] Longtang Yiyong transmigrates into one of Orochimaru's experimental subjects, who is on the verge of death. Unexpectedly, he awakens a “Kill Enemies, Plunder, and Burn Lifespan” System. From then on, killing enemies lets him grow infinitely stronger. Step by step, he carves out an invincible path. Also known as “You Told Me to Burn Lifespan to Get Stronger, So Why Are You Burning Other People's?” and “Friend, Hold On a Moment. Your Ninjutsu and I Are Destined to Meet.”