Seppuku Kuro Usagi functions as a messenger in the Kämpfer universe, personally assigned to Akane Mishima. This entity takes the form of a black rabbit plush, showcasing the Entrails Animal motif through exposed internal organs, bloodshot eyes, and bloodstains around its mouth. Its core duty involves clarifying combat regulations and battle mechanics for Kämpfers under its supervision.

The messenger communicates with sharp sarcasm and vulgar language. Despite this rough exterior, it coordinates effectively with fellow messenger Harakiri Tora. Their rapport emerges during exchanges like a television discussion, where Seppuku Kuro Usagi explicitly demands pay-per-view adult content.