Ryuko is the Hero Nejire is working with for her internship. The two seem to have a close friendship, as Ryuko was willing to listen to Nejire's offer to recruit Ochaco and Tsuyu into her office, and did not object to Nejire throwing her arms around her.
Along with Mirio and Tamaki, Nejire represents U.A.'s Big 3. The three have spent three years together studying at U.A., becoming good friends with one another.
It appears that while all three of them are mutual friends, Nejire seems to be closer to Tamaki than she is to Mirio. Tamaki calls Mirio by his first name, which indicates a special level of closeness in their friendship that Nejire doesn't demonstrate, as she simply calls Mirio by his last name. Nevertheless, Nejire noticeably cares for Mirio, shown when she was actively trying to cheer him up and convince him not to be too hard on himself during his depression over Eri's situation.
She, Mirio, and Tamaki represent U.A.'s Big 3. They have spent three years together studying at UA becoming good friends with one another.
Tamaki treats Nejire's talkative attitude casually with tolerance and would attempt to keep that personality of hers in check when required. Nejire finds Tamaki's anxious personality weird, calling it 'chicken-hearted', which becomes her nickname for him.
Interestingly, she does not seem as concerned for Tamaki when she learns of his attack as Mirio is.
Nejire helped Ochaco and Tsuyu get an internship with Ryukyu. The three established a good relationship with each other since Ochaco and Tsuyu listened and cooperated with Nejire splendidly.
Nejire and Yuyu seem to be close, and Nejire cites Yuyu as the reason she originally entered the yearly Beauty Contest. Yuyu is later seen helping Nejire prepare for the School Festival. Yuyu and Nejire also appear to have matching bracelets.
Yuyu's Character Profile reveals that she is is Nejire's best friend, and that she thinks Nejire is the "cutest thing in the galaxy".