Ep. 3: Tsubaki receives Urabe's saliva to test their romantic connection after witnessing Kouhei with Ayuko.

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Tsubaki observes Kouhei kissing his girlfriend Ayuko Oka, prompting him to ask Urabe for a kiss. She provides a test tube of her saliva, instructing him to drink it before sleep. He dreams of an unfulfilling kiss by Urabe, leading him to believe kisses require mutual understanding. Later, classmate Ogata confesses to Urabe, who delays her response and bars Tsubaki from interfering. The following day, Urabe rejects Ogata after he feels no change from consuming her saliva. When Tsubaki tries the same, he suffers a nosebleed because Urabe was not wearing underwear. She explains this unique physical reaction proves he is the only one sharing this bond with her, and they walk home holding hands.