Chivalrous Costume (任侠衣装) is an item that appears in Mass for the Dead.
During a Yozakura that was hosted by Demiurge, he wore this outfit to display his loyalty to his master Momonga. He intended to wear it as he hosted the event, but found himself in conflict with Sebas Tian who also wore one insisting it reflected not only loyalty but justice.
Basically a kimono, a traditional Japanese garment.
According to the game, it increases physical attack power and physical defense power.
- The name originates from what the Yakuza call themselves ninkyō dantai (任侠団体/仁侠団体, "chivalrous organizations."