Yuusha Party wo Tsuihou sareta node, Maou wo Torikaeshi ga Tsukanai hodo Tsuyoku Sodatetemita  

I Was Exiled from the Heroes Party So I Tried Raising the Demon Lord to Be Unbelievably Strong, 勇者パーティーを追放されたので、魔王を取り返しがつかないほど強く育ててみた

One day, a person named Raizel was unexpectedly called upon to another realm for the purpose of defeating the Demon Lord. Despite being told he had no combat abilities, it turned out that the calculator responsible for determining his combat capabilities made an error and Raizel was actually incredibly powerful. After being exiled from this world, Raizel embarked on a journey during which he came to understand that demons were not inherently evil beings. He then joined forces with them. As a result of discovering valuable information that could significantly alter the current state of affairs in this world, Raizel and his companions set out to overthrow the empire that had initially brought him here.