Nendou calls Kusuo his partner after the day he saved him when Takahashi framed him. Since then, he has been sticking to Kusuo like glue and always asks him out to eat ramen or just to hang out. Kusuo is usually the friend of Nendou who actually think he's a nice guy along with their gang despite having a scary face.
Nendu and Kaidou used to fight as who should be Kusuo's best friend but in the end, the two also got closer and since then went out together with Kusuo. Along with Kusuo, Nendou asks Kaidou out occasionally to eat ramen whenever the school ends.
For Hairo, Nednou for him is a rival in terms of sports and strengths. Nendou is usually lax in terms of Physical Education but Hairou usually challenges him resulting in Nendou winning.
Nendou was first ignored by Toritsuka after thinking he's the ghost that always followed him but after learning that it was his father, the two got friendly.
Aren and Nendou got friendly after Aren started to hangout with their small group.
As the usual reaction, Nendou would always react the way the usual fanboys react towards Kokomi.