The Invincible Bodyguard

Kane, an Avalon Watcher, takes a 90-day mission to protect scientist Lina while uncovering the truth behind his parents' deaths. Lina's Life Tree can regenerate limbs, making her a target for Elden's tycoons. Posing as an ordinary security guard, Kane defeats traitors, assassins, underground armies, and high-tier espers—from knocking down a sniper bullet with a button to single-handedly subduing the Blackstone Alliance—making those who scorned the "country bodyguard" pay and gradually earning Lina's trust and love. When his memory chip unlocks, Kane learns that Cassino, ruler of Devereux, murdered his parents and seized the Life Skeleton—and that Lina is the girl he vowed as a child to protect forever. By then Lina has been kidnapped, and Devereux's underground base is rigged as a death trap. Kane storms the base alone, achieving transcendent awakening under toxin suppression and esper legion siege, destroying the Devereux empire and avenging his parents and the dead researchers. In the ruins, he and Lina recognize each other—from a 90-day protection mission to a lifelong vow.