Takashihe, Yuuhan wa Dungeon no Okudesu

Takashi, who has been living a reclusive life, wakes up one morning to find himself transported to a dungeon overrun with monsters. In front of him is breakfast, which his mother had probably prepared for him, and a letter from her. The letter contains only one sentence. Takashi's adventure begins.

(Source: Kurage Bunch, translated)