Mirko, also known as the Rabbit Hero: Mirko, has a blood type O.
This specific detail about Mirko's physiology was officially revealed in supplementary materials related to the My Hero Academia series. Kohei Horikoshi, the creator of the popular manga and anime, often includes character profiles and additional facts in his published works. The information confirming Mirko's O blood type can be found in Volume 2 of the My Hero Academia manga, which was released in 2019. These official character data books provide fans with interesting insights and expanded lore beyond the main storyline.
