Iwasaki-sensei teaches at the high school where Kyosuke Ichimaru works and Asami Onohara studies. She harbors romantic feelings for Kyosuke, fueling significant conflict. Her pursuit includes frequent social invitations, such as extended tea meetings that evolve into dinners, and a drunken confession during a colleague outing where she attempts to kiss him. Learning of Kyosuke's involvement with another, she grows obsessed, vowing not to "lose to a little girl," and abuses her authority to sabotage his personal life, striving to separate him from Asami. Her actions escalate to repeated blackmail after uncovering his secret marriage to a student.

Motivated by a fear of becoming an "Old Maid"—a trope tied to her unmarried status at age 24—she persists despite Kyosuke's rejections. She further manipulates relationships by trying to set Asami up with her own high-school-aged younger brother. Her arc culminates upon witnessing Kyosuke and Asami together, revealing their secret marriage. This leads to her resignation and eventual acceptance; she chooses not to expose them, embodying the "I Want My Beloved to Be Happy" trope by guarding their secret. The anime adaptation portrays her as less antagonistic than her manga counterpart, where her disruptive and manipulative behavior remains consistent.