Tsuyu has a good relationship with her family, especially with her younger siblings, Samidare and Satsuki. Due their parents, Ganma and Beru, often work away from home, Tsuyu was the one who takes care of them by herself, doing things such as making them dinner.
Tsuyu respects Izuku for his heroic actions as well as his victory against Katsuki. In their first meeting, she had noticed the similarities of his powers and All Might's but is given a vague answer by him.
During the U.S.J. Arc, she saved him from being attacked by villains and was receptive of Izuku's plan to subdue the swimming villains, showing not only respect, but also trust. In return, Izuku was quick to try and save her from Tomura Shigaraki who nearly killed her but Shota Aizawa and All Might saved them.
Interestingly, Tsuyu repeatedly tells Izuku to call her "Tsuyu" rather early on in their knowing of each other. He appeared to be the first person she was fine calling her by her first name, repeatedly reminding him to call her that every time he forgets or automatically calls her by her surname out of politeness. Considering Tsuyu has gone on to say she only wants people she considers, or wants to be a friend to call her that, it is clear that Tsuyu views Izuku as such. While Izuku seems to call her "Asui" more often than not, due to his polite personality, he has called her Tsuyu on occasion, and has shown concern for her, meaning he views Tsuyu in the same light.
When Tsuyu broke down crying after apologizing to everyone for questioning the plan to rescue Katsuki, Izuku felt bad for putting her through the pain and they reconcile.
Tsuyu and Ochaco are close friends, as they are on a first name basis with each other. During the Forest Training Camp Arc, Tsuyu comforts Ochaco by offering to hold her hand, which Ochaco accepts. They fought well together against Himiko Toga and Ochaco was concerned for her after Tsuyu was attacked.
When Tsuyu broke down crying after apologizing to everyone for questioning the plan to rescue Katsuki, Ochaco comforted her by holding her.
Tsuyu is frequently seen together with Minoru, although she constantly punishes him for his perverted behavior or insensitive comments. Tsuyu often scolds him by hitting Minoru with her tongue.
However, the two seem to be on friendly terms, to a degree as she rescued him from villains in the U.S.J. Arc and was impressed with his quick thinking. They also paired up together during the sports festival showing they work well together despite their conflicting personalities.
Although their interactions in the classroom have been minimal, Tsuyu has been paired with Fumikage a number of times. They worked together during the battle trial and the practical section of their final exams.
Tsuyu and Fumikage agreed to strategize prior to their practical exam, showing they had strong communication with one another. During their test against Ectoplasm, Fumikage and Tsuyu displayed elite synergy and teamwork. Their Quirks work very well together in both evasive and combat situations. Tsuyu provided support while Fumikage did the bulk of the fighting. Although they were overwhelmed by Ectoplasm, Tsuyu believed they would be fine because Fumikage is strong. Together they managed to pass their finals.
The two girls are friends, as they are often seen talking to each other. Tsuyu congratulated Mina for making it to the tournament, even though she was angry about her own failure. Mina was shown to be amazed by Tsuyu's internship and called her time there cool.
Nejire helped Ochaco and Tsuyu get an internship with Ryukyu. The three established a friendship with each other since Ochaco and Tsuyu listened and cooperated with Nejire splendidly during their internship, as well as when Ochaco and Tsuyu fought against Himiko Toga.
Tsuyu teamed up with Shinso, during the first round of the Joint Training Battle. After the initial clash with the Class 1-B team, Hitoshi apologizes for his lack of battle readiness but Tsuyu replies that was her fault because she should've come up with a better plan to keep him off the front lines. After winning the round, Tsuyu recognizes Hitoshi's combat ability and strength, praising him and asking him to forget what she said before about being behind. Hitoshi responds to Tsuyu's praise by saying he still has much to improve.
Tsuyu gets along very well with the Oki Mariner crew, especially with the captain Selkie and his sidekick Sirius, with whom she trained alongside in the internship. Sirius taught Tsuyu the importance of becoming a hero and agreed that she will become a great hero one day. Due to her inexperience and that she is not yet a Hero, Selkie tries to avoid Tsuyu being involved in hero works, but congratulates her when she does the right thing in a dangerous situation. Tsuyu seems to be the only one who finds adorable the captain when he attempts to making himself look cute.
Thanks to Nejire's recommendation, Tsuyu, along with Ochaco, is hired by "Dragon Hero" Ryukyu for internship. Tsuyu respects the Pro Hero and is grateful that she accepts her as an intern. On the other hand, Ryuko thinks that she has potential, and that the internship will help to develop her fighting skills.
Ryuko relies enough on Asui's abilities to consider her fit to participate in the raid against the Shie Hassaikai. During the operation, along with Ochaco and Nejire, Tsuyu helps Ryuko to defeat Rikiya Katsukame.
Tsuyu and Himiko are enemies. Tsuyu greatly dislikes Himiko for aiding in the League of Villains' attack on the camp, as well as attacking her and Ochaco. Tsuyu considers her to be crazy because of her behavior in their meeting. Despite Himiko's attempts to befriend her, Tsuyu reacted with displeasure, especially when Himiko called her by her first name, since that's something only her friends are allowed to do.
Habuko was a student who attended the same middle school as Tsuyu and was the first friend Tsuyu made. They had many similarities to each other; having strange appearances that made it difficult for them to make friends and they were lonely individuals as a result. Often, Habuko would stalk Tsuyu but not with ill-intent. Tsuyu did not mind this because she understood Habuko's loneliness resulting from her appearance. Eventually, Tsuyu asked to be friends with Habuko. Touched by her kindness, Habuko agreed to be friends with her. Ever since, the pair were close to one another.
They graduated from middle school together, but went to different high schools. Even though they are at different high schools, Tsuyu and Habuko never stopped being friends with one another as shown when Habuko sent her a message and Tsuyu herself notes that Habuko will always be her friend; their friendship became a catalyst that helped them socialize more and make new friends from their respective high schools.