Forgot name

Can somebody help me find the name of this one bl that was similar to a apocalypse and in a guideverse setting. The mc have black hair and the ml had tanned skin. From what I can remember the beginning starts where the mc gets acceoted into this safe institution by passing a test (to see which I don't think it's especially but let's say esper ability is better). There he's with another dude with a brother and the people there test him seeing if he'll give up his spot for the brother. I remember the mc having a plant based ability where he just smells like medical plants. For the male lead, I remember that his backstory was being on this island along with another kid (I think blond) where they would battle zombies as children without knowing that. I'm pretty sure the zombies were their friends who just died? I don't remember much but I do know that mc is the lead to ending the virus/apocalypse eith his plant ability and the institution is aware of this (hence why they test him so much). If anyone could PLEASE find me the name that'll be very much appreciated!! (P.s the series is completed!)