Koke kara Hajimaru Isekai Life

Hikaru, who died at just 20 years old, was granted reincarnation in another world by a goddess's mercy. But due to a mistake, he wasn't reborn as a human; he became moss! “I'll die for real if I don't do something!” Terrified to begin his new life as the weakest possible creature with abysmal stats, Hikaru strategizes how to survive using his rebirth bonus: Additional Skill Acquisition. As he defeats nearby small animals with his chosen skills and newly learned magic to grind levels, he makes an incredible discovery: his moss form can evolve into other species.

(Source: Kadokawa, translated)