Kage ni Kakureteta Ore ga Maougun ni Haitte Hontou no Shiawase wo Tsukamu made

I found real happiness ≪here≫ in the demon lord's army. Cromwell, who held his abilities back while hiding in his flawless best friends' shadow, was one day taken to the demon lord's army. Getting "serious" he does things like, reforming the demon lord's army while living together comfortably with his succubus secretary and a little demon girl.