The world's finest Assassin accepts the Goddess' request to assassinate the Hero. After defeating the Demon Lord and saving the world, the Hero will then use his power to destroy the world. The Goddess wants the Assassin to be reincarnated in another world and assassinate the Hero in order to save it. After being betrayed and killed by his client in his previous life, the Assassin accepts her offer in order to relive his life in a new world, but--
But I can still strengthen 
my mana by doing this.
لكن حتّى الآن، يمكنني تقوية المانا
Jedoch kann ich mein Mana
auf diese Weise trainieren.
Pero no poder usarla
no me impide fortalecer mi maná.
Par contre,
rien ne m’empêche de m’entraîner.
Posso comunque allenarmi nell'uso
della magia in questo modo.
Mas mesmo agora, ainda
posso fortalecer meu mana.
Но даже так я могу 
усиливать свою ману.