Fei Tu Yu Anxi

An Xi grew up in a radiation shelter, and never met an outsider until he turned 16. The mysterious outsider is strong and tall, and An Xi can't take his eyes off him. When An Xi was attacked by a mutant invader, the outsider saved him and they formed a friendship. An Xi made up a name for him — Fei Tu. And then Fei Tu shared his secret with An Xi…

(Source: Bilibili, translated)