Jashin no Mago - Dark Elf Shimai to Sugosu Isekai Hikikomori Seikatsu

Shut-in Satoshi Katakura supports himself with investment income from his grandmother’s inheritance. One day, he wakes to find an otherworldly realm spread beyond his home, and two dark elf sisters appear before him, revering his grandmother as the Evil God. The sisters pledge eternal loyalty to Satoshi and call him their master. Their true purpose and the real identity of his grandmother remain questions as he begins a shut-in life in another world with them.