The Duke's Good-for-Nothing Son Is Actually the Hero in the Shadows, and That's No Secret

Hitobito wo Kagenagara Sukutteiru Eiyuu, Jitsu wa Koushakuke no Kuzu Musuko. To Iu no wo Shuui wa Shitteiru / 人々を陰ながら救っている英雄、実は公爵家のクズ息子。というのを周囲は知っている / The Hero Saving People in the Shadows is Actually the Duke's Scoundrel Son (The People Around Him Know)