18+ Keiken wo Skill ni Suru Bannou na Nouryoku wo Te ni Irete, Saikyou no Tansakusha ni Narimashita: JK to Issho ni Dungeon Tansaku de Nariagaru

Masato, the eldest son of the Jingu family, begins working as an explorer in the “Tokyo Dungeon” to support his younger brothers after their parents pass away. However, recognizing the limits of working alone, he decides to look for companions to help conquer the dungeon. That is when his younger brother Rekka introduces him to Rika Tachibana, and the two form a party. They encounter many hardships along the way, but as they support each other and overcome those challenges together, their bond gradually grows deeper...!?

(Source: Nihon Bungeisha, translated)