Isekai One Turn Kill Nee-San異世界ワンターンキル姉さん　～姉同伴の異世界生活はじめました～

You know that one series where the main character gets sent to another world, but his mother gets sent with him, and she’s super overpowered but also really doting to the MC? Yeah, replace “mother” with “big sister” and you have a good idea of what this series is about.