Inmates
Jyugo
While the their relationship is not properly explored, it is shown Jyugo gets along with Nico. Nico admires Jyugo's lock breaking skills, calling him amazing. Jyugo seems to see Nico as a little brother and worries for Nico since he seems to get into trouble easily.Rock
The two seem to be best friends as the two interact with each other more often than the others. When the they met Jyugo at Las Vegas, the two of them were traveling together. They are both the less intelligent members out of their friends and get along well, though Rock once referred to Nico as a pet.Uno
While the two don't interact much, they are shown as good friends. Uno acts as an older brother to Nico and once helped him order some anime figurines online for him, something Nico was grateful for. They also make friendly bets with each other. The two both share some artistic talent and enjoy joking with each other.Upa
At the first meeting Nico was highly impressed of Upa's qigong skills and was so glad to meet him again on the tournament. Nico wished to become his disciple with all heart, but Upa didn't see the talent and potential in him. Upa was annoyed of Nico's levity and “petty goal” and refused him every time. Despite that, Nico still kept asking. Upa tired of it and was ready to kill Nico, but Nico's desire to become disciple was much stronger and thus he won.
After the tournment, Nico still likes Upa and acts very friendly with him. Nico calls him "master" despite not being his disciple, hugs him when meets
Guards
Hajime Sugoroku
While the two don't have much interaction, Hajime tends to get annoyed with him like he does with the other Cell 13 inmates. However, he also refers to Nico as a good kid and the easiest of the cell mates to handle, and seems to treat him slightly gentler than he does the other inmates due to being one of the youngest and least threatening. Nico acts friendly to Hajime though he does tease him on occasion.Seitarou Tanabata
Like the other inmates in his cell, Nico has been shown to tease and throw things at him when he makes his rounds, along with scaring him by sticking out his tongue and making faces at him. Other than that, Nico appears to think well of Seitarou as in season 2 when he held a bag that Seitarou had specifically sewn for him he became sad thinking of him.Yamato Godai
Not much is shown other than Nico disliking his training and hiding under the matress along with Uno, Rock, and possibly Jyugo.