Sekai Ichi Hatsukoi: The World's Greatest First Love: Go to the Sea, If You Would Fish Well.

After an onsen trip, Chiaki is burned out and can hardly concentrate on work. The emerging love triangle between him, Hatori and Yuu compounds his inability to focus as well. Later on in Chiaki's apartment, Hatori informs him that he must attend an upcoming party because his manga will be made into an anime and he must meet the people in charge. Hatori offers to pick a suit for Chiaki, but Chiaki prefers to go shopping with Yuu instead, sparking jealousy in Hatori. After Yuu leaves, Hatori makes tries to kiss Chiaki, upon which Chiaki pushes Hatori away because he feels that Hatori is moving too fast. This upsets Hatori and he leaves. During the party, after meeting the anime staff, Chiaki sees Hatori surrounded by many women, including Ichinose Erika; a top writer who is known to have taken a liking to Hatori. Chiaki, feeling that Hatori is comfortable with the writer, becomes jealous and promptly leaves the party with Yuu. Hatori eventually arrives at Chiaki's place because he still needs to discuss some corrections with Chiaki's manga. Chiaki smells perfume on Hatori; feeling that the writer at the party may have gotten too close him, he becomes angry. Hatori reassures Chiaki otherwise and also confesses his jealousy about Chiaki and Yuu, feeling that Chiaki favors Yuu over him. Chiaki also reassures him and Hatori tells him that he loves him, and will continue to tell him until he can never forget. The morning after, Yuu admits to Chiaki that he is in love with someone, but when Chiaki asks who the person is, he simply says that Hatori knows the person well, leaving Chiaki puzzled and confused.