Hazure Skill Level Up no Sei de Party wo Tsuihou Sareta Shounen wa, Level wo Agete Butsuri de Naguru

At the age of 15, everyone is gifted with a talent - "skills." Chamber was a member of Akatsuki, a party made up entirely of young members that had distinguished itself in the city, but he was expelled from Akatsuki after obtaining a mysterious skill called "Level Up," whose effects are unclear...! Although abandoned by the other members who had obtained powerful skills, Chamber continues to work as a solo adventurer. It was during this time that he discovered the true value of the skill known as "Level Up." "The more enemies you defeat, the higher your level becomes and the stronger you become." After realizing that his skill was not just a "useless skill," Chamber has a fateful encounter with a certain girl and begins to spend his days pursuing strength...!

(Source: Kodansha, translated)