Level 1 Kara Hajimaru Shoukan Musou: Ore dake Tsukaeru Ura Dungeon de, Subete no Tenseisha wo bu Chigiru

It couldn't get any worse for Shinobu Iijima. After a terrible house fire consumes his life and puts his sister, Megumi, on her deathbed, Shinobu wakes up in his favorite MMO: La Vita Online. With all his data deleted and reset back to level 1, the only solace Shinobu has is that his scumbag of a foster father, Ayumu, died with him...only to discover he was reincarnated in the game as well?! A nightmare reborn, Ayumu pledges to get revenge on the siblings, biding his time until Megumi eventually dies and reincarnates in La Vita. While Megumi struggles through her last breaths in the real world, Shinobu does his best to grind his way back up the levels before her reincarnation. Armed with a hidden dungeon, his hard-earned legendary summons, and an undefeatable will, Shinobu must reach the max level in order to protect his sister from their foster father and the other reincarnators threatening to stop him at all costs. (Source: J-Novel Club)