Yakumo Koizumi is a researcher born in Greece who journeyed to Japan, adopting the name Koizumi Yakumo – "Yakumo" translating to "eight clouds." His path led him to teach English and study Japanese spirits, the mononoke. After leaving Greece, he grew up in Ireland, fostering a deep appreciation for Japanese culture while retaining his foreign roots. He stands 185 cm tall and wears an eyepatch over his left eye, often joking it holds "the power of darkness." His spoken Japanese includes occasional anachronisms and grammatical quirks, reflecting his non-native fluency. Professionally, he lectures in English at Tokyo Imperial University, yet his true passion lies in researching supernatural entities. He actively gathers information on mononoke day and night. Outwardly cheerful and gentlemanly, he harbors a mischievous streak, delighting in telling unsettling ghost stories. He holds a distinct dislike for Western cultural influences. His supernatural expertise proves vital in narratives involving time travel or spirit encounters. He collaborates with those who see spirits, like Mei Ayazuki, offering guidance on navigating mononoke. He sometimes exhibits protective instincts, especially concerning spirit-related safety. Significant abandonment marked his youth, contributing to his complex worldview. Despite a generally composed demeanor, he displays flashes of jealousy or possessiveness, such as opposing romantic relationships he deems unsuitable. His hobbies include sea bathing, and he commands proficiency in multiple languages. His narrative role often involves mediating between the human and spirit realms, leveraging both academic knowledge and personal fascination with the paranormal. He moves within Meiji-era social circles, where his foreign perspective and supernatural expertise frequently shape group dynamics.