I’ve Been Killing Slimes for 300 Years and Maxed Out My Level

Slime Taoshite 300-nen, Shiranai Uchi ni Level MAX ni Nattemashita
スライム倒して300年、知らないうちにレベルMAXになってました

Source

I've Been Killing Slimes for 300 Years and Maxed Out My Level
Slime Taoshite 300-nen, Shiranai Uchi ni Level MAX ni Nattemashita· スライム倒して300年、知らないうちにレベルMAXになってました
novel
Tapas Yen On
and 2 more

After living a painful life as an office worker, Azusa ended her short life by dying from overworking. So when she found herself reincarnated as an undying, unaging witch in a new world, she vows to spend her days stress free and as pleasantly as possible. She ekes out a living by hunting down the easiest targets - the slimes! But after centuries of doing this simple job, she's ended up with insane powers...how will she maintain her low key life now?! (Source: Yen Press)

Side Story

I Was a Bottom-Tier Bureaucrat for 1,500 Years, and the Demon King Made Me a Minister
Hira Yakunin Yatte 1500-nen, Maou no Chikara de Daijin ni Sarechaimashita· ヒラ役人やって1500年、魔王の力で大臣にされちゃいました
manga

For 1,500 years, Beelzebub has happily taken. it easy as a rank-and-file clerk. But her lazy lifestyle comes to an end when the new demon king suddenly promotes her to minister! Can she adopt the appearance and demeanor expected of the highest demon on the bureaucratic pyramid? *Source: Yen Press, Vol. 1*

Side Story

I’ve Been Killing Slimes for 300 Years and Maxed Out My Level Spin-off: The Red Dragon Academy for Girls
Slime Taoshite 300-nen, Shiranai Uchi ni Level MAX ni Nattemashita Spin-off: Red Dragon Jogakuin· スライム倒して300年、知らないうちにレベルMAXになってました スピンオフ レッドドラゴン女学院
manga

Challenge, victory, growth! To become the strongest dragon and surpass her older sister, Laika starts attending an elite academy for dragon‐girls. However, even though it is only the first day, she has somehow managed to find all kinds of trouble… *Source: Yen Press, Vol. 1*