As a moments page, all spoilers are unmarked, as per policy!
The early confusion between Takeo and Yamato, while amusing at first, becomes sadder and sadder as it goes on. Takeo, despite clearly having feelings for Yamato, is utterly convinced that no girl would ever fall for him, and that Yamato is in fact, in love with Suna. Truthfully, she's in love with him, and keeps trying to get to know him and do nice things for him while he, thinking he's doing her a favor, keeps trying to play matchmaker between her and Suna. It eventually escalates to the point where he basically gives her his blessing and best wishes for their happiness, again, completely oblivious to her feelings. Yamato's so hurt by hearing this from the man she actually loves, she runs away crying.
Takeo tells Yamato about a play that he and Suna starred in when they were kids about a pair of ogres. The Red Ogre, played by Takeo, was feared by the people in the nearby village and caused him to feel sad and lonely. The Blue Ogre, played by Suna, offers to help him by pretending to attack the village which would allow the Red Ogre to come in and "save the day". The Blue Ogre's plan works and the Red Ogre is accepted and beloved by the other villagers. After some time, the Red Ogre notices that he never sees the Blue Ogre anymore and goes to his house. He finds a letter where the Blue Ogre states that if he continued to be friends with him, then the villagers would mistrust the Red Ogre. The story ends with the Red Ogre crying about how his friend left him without saying a word.
Yamato overhearing her friends saying awful things about Takeo behind his back. She's truly crushed by how cruel they were, and bursts into tears while insisting that Takeo is indeed handsome. She then runs out of the building, hurt and embarrassed by their behavior.
Poor Ai. She had a crush on Takeo for years, but held back due to the three-year age gap, and decided she would wait until he got to college before she made her move. And then Takeo gets himself a girlfriend. A wonderfully cute girlfriend who Ai can't even hate because she's just so nice, and her and Takeo make such a great couple. Ai has to leave right after helping Takeo and Yamato through a misunderstanding, so that they won't see Ai crying. And even after claiming she has moved on, the signs show that Ai is still hurting from the heartbreak a lot.
Saijou's crush on Takeo. It's sad because Saijou knows her feelings are unrequited, and that Takeo and Yamato are head over heels for each other, but can not resist taking advantage of Takeo's density and Yamato's kindness to spend more time around him. Eventually she decides to confess properly, and Takeo has to turn her down. Fortunately Suna's on hand to provide a box of tissues.
Yukika Amami's crush on Sunakawa falls hard under here. Unlike the usual people who very shallowly fall for Suna's good looks; Yukika's been in love with Suna since Kindergarten, but has been unable to even approach him on her feelings. She finally works up the courage to confess to Suna (or not, seeing as she let it slip), leading to a double date on the next episode. But after that, she realizes that Suna simply doesn't love her the same way, and begins to regret ever confessing to him. What makes this even harder is that the main reason why Suna's never accepted any other girl's feelings is because they'd badmouth Takeo behind his back. Yukika, on the other hand, never did such things. Thankfully, Suna is more than happy to thank Yukika for her anonymous packages, and although they won't hook up, they can still be friends.
Takeo's justified reason for being initially Oblivious to Love. The fact that he's been judged by most people all his life due to his less than average looks makes his relationship with Yamato and Suna all the more heartwarming.
Yamato's encounter with the groper. She's crying and terrified, having no idea what to do.
Suna's father's hospitalization. It's made even sadder with a flashback to Suna as a young kid, sitting sadly on a swing because that was the first time his father had the operation. And then the fact that (present-day) Suna blames himself for the medical troubles because he didn't come home right away after school. Luckily, Takeo was there both times to cheer him up.
Suna, when babysitting infant Maki in the park, tells her that Takeo has grown and changed so much, recently and seems to be spending less time with him and drifting apart. And while he claims he doesn't need somenoe to follow him, he admits he's lonely. Thankfully Takeo overhears him and proceeds to rectify the situation with some one-on-one time at a local onsen.
Suna being jealous of Takeo during middle school in an omake in volume 12. He's jealous because of how Takeo's body is changing (becoming stronger, deeper voice) - all the while he's still complimented as a handsome man, but it's obviously not what he wants to be.
