The slow progression of the new relationship of Bossun and Tsubaki, after they find out that they are twin brothers, and how they start getting more and more along with each other:
One day, Akane invites Tsubaki to eat dinner with them, as she wanted to meet the other child of her best friends, Ryosuke and Haru Kirishima. She even remarks that while Bossun looks more like Ryosuke, Tsubaki looks similar to Haru, as he shares the same eyelashes from her. When the twins are watching Ryosuke's home movies, Tsubaki cries out of happiness as he is very glad that he met his biological parents through them. They eat dinner together and share the same table, and then they finally take a picture together. They might be standing with a distance between them, but they are taking baby steps.
When Tsubaki wants to defend Daisy from some blackmailers, he asks Bossun for some advice about the situation. And even if he wanted to do it for himself, the Sket Dan helps him afterwards (they go as "unwanted" back ups, poorly disguised, but they are a necessary help).
Agata tries to indirectly ask Tsubaki about his relationship with Saaya... only for Tsubaki for think he's asking about Bossun. Although the resulting conversation is Played for Laughs because of Agata misunderstanding everything, it's sweet to see that Tsubaki is uncertain yet genuinely interested in getting close with his brother and values the connection they share.
Tsubaki admits little by little that Bossun is becoming a greater influence on his life, such as that time he wanted to do coordinated t-shirts for him and the rest of the Student Council.
Tsubaki is once called over by Rumi to snap Bossun out of his JRPG addiction. What happens instead is that Bossun teaches him about the game (since Tsubaki's never played video games before), and the both of them end up getting addicted playing together. They team up both in the game and then out of the game when they defend themselves against a wild dog as if they're still playing. After that brief moment of bonding and excitement, the two of them get embarrassed and go back to their homes, acting like it never happened.
During the chapter when Tsubaki gets turned into a kid in body and mind, Switch notices that Bossun's affection towards him totally goes off the charts. He also gets his now-little brother to call him onii-chan — after Tsubaki is turned back to normal (and has no memory of the incident), he accidentally addresses Bossun this way, much to their embarrassment.
Himeko once berates them for still being on a Last Name Basis, and the two show little interest in acting any chummier than that. However, after successfully getting successors for their respective roles at school, the two decide to start going on a First-Name Basis. The two seem pleased with this after first awkwardly trying it out, and they continue to refer to each other as Yuusuke/Sasuke until the end of the series.
Any time when Switch shows that he really cares about Reiko, despite their different arguments about Occultism vs. Science, and the fact that they deny that they are "friends".
When he is helping Reiko to get a new computer, one of her old classmates shows up and immediately recognizes her, as he tells her that he isn't surprised that she hasn't changed at all ever since middle school. This makes Reiko self-conscious about being "weird", as Switch was previously telling her about how she could improve many things about her self-image. When she asks for his advice, he replies that she is "okay" and that if she was just a normal girl, he wouldn't be more weird than she is, apparently. He lends her a hand to get revenge on that guy, while also giving Reiko a make-over that would make her feel beautiful even if it would be for one time only.
Switch helps her with the whole Fortune Teller incident, as he explains to Bossun and Himeko that he wouldn't like to see her influenced by the Fortune Teller, because "she wouldn't be herself".
In Chapter 181, Reiko wants to do a film for a horror film contest so she can get more views for her website, and she wants the help of the Sket Dan to shoot it. Switch, a horror movie fan, reluctantly says that he won't do it while Bossun and Himeko gladly help her, but at the end he gives up and takes the seat of the director since he can't stand the terrible job they're doing. Despite his bossiness, his efforts pay off and end up being a big help with their entry getting first place — although it ends up being counterproductive as it scares people away from Reiko's website.
Just after Momoka clears up the Onihime's impostor incident, she helps the Sket Dan to do a show for the kindergarteners (as part of a challenge/punishment from the Student Council, since she and her friends weren't supposed to be on Kaimei's school grounds after-hours, as she wasn't a student from there). They finally decide to do a puppets show based on her experience with them, and she has the role of the narrator. As long as the narration goes, she can't hide her feelings about the story's parallels to her own, when she met Himeko and the Sket Dan, as it helped her realize that she was glad that she met them, since she also needed new friends.
During the Kaimei Rock Festival, the Sket Dan (as The Sketchbook) does a cover of The Pillows's "Funny Bunny" dedicated to a new friend of Bossun who is a violinist, as she was close to give up her dreams of being a professional musician. It motivates her enough to keep studying music abroad.
The finale of "Ogress" offers a few moments regarding Himeko's past and present:
When Himeko reveals that she is Onihime, neither Captain nor Bossun want to distance themselves from her, and they accept her for the person that she is. Bossun even tells her that he needs "her" to form part of his idea of a club helping other people.
Himeko gives a narrative speech about how her hero, who used to be her favorite TV character, appeared before her ("dripping with sweat") and rescued her, despite the fact that she was a delinquent. She ends up crying on Bossun's shoulders.
In the present, Himeko reconciles with Arisa after she apologizes for all the problems she caused her.
The beginning. It first shows a compilation of short video camera clips of Bossun and Rumi growing up, with many adorable sibling moments (such as Bossun holding baby/toddler Rumi's hand, the two of them doing the Popman pose together and Rumi laughing at Bossun's robot imitation). It then shows Akane hugging her two kids, with Bossun looking a little annoyed at first but then smiling and blushing afterward.
For the episode after Bossun and Tsubaki's backstory and relationship is revealed, the opening changes the ending scene to a picture of Ryousuke, Akane and Haru happily gathered together — with Ryousuke holding baby Tsubaki and Haru holding baby Bossun, while Akane playfully pokes Bossun's cheek.
Bossun, who always struggled knowing that he was adopted and that his blood relatives were deceased, finds out that Tsubaki is his twin brother in "Happy Rebirthday". They manage to calm down their rivalry differences and accept that they are siblings, while also accepting that their relationship isn't going to change from one day to another. They wish to each other a happy birthday afterwards. But the touching moment happens later when he walks alone after the closure of the Culture Festival, and realizes that he isn't alone anymore.
The farewell rally plan that the Student Council organizes for Agata (with Bossun's help), as he was leaving his President position. The anime even goes further offering a song performed by the Student Council's voice actors as the ED theme of that episode.
During "Christmas Card", the Sket Dan has to deal with Morino, a friend of Fumi Segawa, who is a hikikomori that decided to stop going to school because he felt that his art was worthless. Knowing that their own Switch was one too one year ago before the events of this chapter (and that he was also difficult to drag out from his house), Bossun and Himeko decide to help him, too. With the experience beforehand, they know that Morino isn't going to be easy to help, since it's up to the person to decide if they still want to be a shut-in or not. They, then, decide to show their feelings, that "he isn't alone", and that "they are his allies". There doesn't seem to be a way to do so, unless they apply something that would motivate him to get out from his house: doing a Christmas Card. It's emotional in a way, because it's not only the Sket Dan who do it, but their friends as well. And guess what? At the end, it ends up motivating him to get out from his house and keep doing his art.
The graduation ceremony of the third years (Agata and Shinba's generation):
Tsubaki gives some final words to the third year graduates , and he ends up crying in the middle of his speech because it is more dedicated to Agata. He, however, stands up and tells Tsubaki to stop being too serious about the speech (since he is doing so as the President of the Student Council) and that he can say whatever he wants to tell him.
When it is his turn, Agata gives his (improvised) Valedictorian speech as a reply to his juniors.
"(...) I have only one thing to say. Regret nothing. Take responsibility for the way you spent your time! Only fools regret! When you're just having fun, you could get to know more friends! 10 years down the road, your experience at your part-time job could come in handy! How you spend your three years here is always your choice! I'll kick your ass if you complain about how boring your school life was! Never look back! Look forward! Move forward! Move forward! Move forward and don't look back!
At the student council orientation camp (with the lineup including Kiri and Usami), as a group activity Tsubaki wants everyone to make matching t-shirt designs for them to wear. The first try fails, with everyone coming up with designs no one can agree on. The end of the chapter however shows that the group did agree on one in the end, with everyone wearing t-shirts with the student council initials and mascot on them.
Chuuma, Remi and Bossun visit the Misora family to ask for Remi's dad's approval for the marriage, since he's skeptical of Chuuma's age and widower status. After some struggling, the dad sees that Suzu is enough proof that Chuuma is a good guy. Defeated, he tells Chuuma to bring his only daughter happiness. Chuuma replies, "With my life."
Switch's first time talking to Bossun and Himeko in chapter 286, and the Group Hug after that with them (including Switch!!) laughing while tearing up is sure to tug one's heartstrings.