At some point prior to becoming a teenager, Mukuro disappeared while she and her family were on vacation in Europe where she joined the elite mercenary group based out of the Middle East named Fenrir Mercenary Group, who engaged in direct combat. During her time spent in the group, she never received a single injury on the battlefield, and received a wolf tattoo as all members of the Group were required to have. She also travelled to at least one other country during her time spent.