Tensura Nikki That Time i Got Reincarnated as a Slimeslime diary That Time I Got Reincarnated as a Slime, Tenura nikki tensei shitara slime datta ken, Tenura nikki tensei shitara suraimu datta ken, 転スラ日記 転生したらスライムだった件
This talks about Rimuru and his friends spending their free time doing something fun together. A spin-off from the main series "That Time I Got Reincarnated as a Slime"