The Zombie Island -osanagocoronokimini- 'link' -

In a quarantined archipelago where adults regress into their happiest childhood memories before mutating into feral, idealized "Child Zombies," a grizzled virologist must return to his abandoned hometown—an island resort frozen in the year 1999—to find a cure. But the final boss is not a monster. It is his own eight-year-old self, who still believes the world is safe.