Yami Zokusei Dakedo Kyakkou wo Abite mo Ii desu ka: Tsuihousareta Shounen Asashin wa Wakeari Yami Bishoujo-tachi to Shin no Yuusha ni Nariagaru

Noel Wraith the assassin is the only party member with dark affinity in the Hero of Light's party. While his party members initially claimed this doesn't bother them, he finds himself kicked out as soon as a replacement for him is found. Left alone in a world where dark affinity is shunned he comes across Rococo, a little girl who also has dark affinity powers. He decides to take her under his wing and together they start their own party to show the world what dark affinity classes are really capable of! (Source: Mangamo)