Shun went on great lengths just to befriend Kusuo. Because of his past as a nerd boy, he sees Kusuo who has no friends a good compatible as a friend so he tried to make him join into his chuunibyou antics but the latter didn't budge. He went on Kusuo's neighbour just to find the alien on his drawing which was actually Kusuo. In the end, Kusuo had no other choice but to show up with the face of the person in his drawing. Shun then started following him around, much to his annoyance.
Shun and Riki the moment they met, started fighting on whom will Kusuo go with (the latter however had never compromised to go to neither the two). At first, Shun doesn't get along with Riki whenever they go to ramen however, it is later shown how the two got friendly constant together when inviting Kusuo to hangout somewhere else.
Shun was the second person to know about Aren's secret of being a former delinquent. Once when he saw Aren with a group of delinquents, Shun then concluded that he is a delinquent too and so he never wanted to befriend him. He was then scared of Aren but later on went friendly with each other after Aren saved him and Kusuo from delinquents who tried to steal their money.
Like any other fanboys, Shun would always react the way Kokomi predicts. Kokomi's effect was strong that when Shun said something about his powers to her and she said she don't understand the reason for the bandages, he right away removed them from his hands curing right away his chuunibyou. In the later chapter, it was hinted that Shun may realize that Kokomi have feelings for Kusuo when he baited Kusuo's name just to make Kokomi come with them at the cruise ship.
Shun's mom is particular with school and studying hence the reason why Shun have good grades. She is also strict and snaps at him whenever she thinks that he's slacking off. She seems to not know about Shun's chuunibyou since he tries hard to hide it.
When he was just a freshmen, Shun met Mineo at the time when Shun was in his initial stage of chuunibyou, Mineo gave way on his creation of his alterego Jet-BlackWings . He felt great shame when Shun, who was called to speak for him in the graduation, recalled their good times as chuunibyou fighting for the world.