Yasumasa Teratani, a high school student and Ichitaka Seto’s closest confidant, dons a nerdy exterior and an unsuccessful romantic history yet boldly proclaims himself a dating guru. He dispenses earnest but misguided advice to Ichitaka on navigating female relationships, his overconfidence and boundary-pushing tactics routinely sparking awkward or counterproductive results. Brash and unfiltered, he cloaks his social missteps in humor and suggestive quips, his self-assured swagger masking a flawed grasp of romance. His candid, tactless remarks occasionally wound others despite their humorous intent, while his mischievous inclinations subtly sway Ichitaka’s actions.

As Ichitaka grows self-reliant in his romantic endeavors, Yasumasa’s prominence recedes, paralleled by his turbulent arc with Yuka Morisaki. Their fledgling relationship, initially steady, frays when he impulsively rebuffs her during a pivotal clash, only to mend tentatively by the story’s end. Beneath his comedic bluster lies steadfast loyalty: he intervenes decisively to shield Ichitaka during crises threatening Iori Yoshizuki, exposing his deeper capacity for empathy. Familial hints suggest his boisterous persona may be hereditary, with male relatives echoing his blend of bravado and boundary-blind antics.