Blakiston's Fish Owl (also known as Blakiston's Eagle-Owl; Bubo blakistoni) is an endangered species that inhabits northeast Asia. Blakiston's Fish Owls were rare (approximately 70 individuals) on Hokkaidō, Japan, at the start of my study, but rigorous protection and intervention programs have led to more than a doubling of the population (approximately 165 individuals) since 1970. Despite its elusive nature and rarity, I have studied this owl species by direct observation and banding for 46 yr throughout Hokkaidō. I here report on little known aspects of its intraspecific interactions and breeding behavior (specifically, pair formation). Identification of individual birds was facilitated by color-banding (a total of 447 owls from 1985–2019). Most pair formations began with an individual male or female flying into the territory of a single owl of the opposite sex, duetting with the resident owl, and then the pair flying together through the forest. However, pair formation occasionally occurred by displacement of a member of an established pair; in some cases, a replacement male took over parental duties. Under government permit, I cared for injured owls, which were housed in large outdoor aviaries; these captive owls sometimes attempted to form pair bonds with wild birds in the area. To test the feasibility of “matchmaking” to increase the number of territorial pairs on Hokkaidō, I attempted to induce pairing of releasable captive birds with wild birds, or to release them into territories with single adults; these tests resulted in successful pair-bonding of the target birds in two cases. I here describe these observations of intraspecific interactions and pair formation to aid future conservation efforts for this endangered species.