Tenya has a very good relationship with his older brother, Tensei. Tenya looks up to Tensei and sees him as a role model, aspiring to be like him. When Tenya finds out that Tensei is critically injured, he leaves the Sports Festival (despite knowing he could receive a medal) and rushes to see his brother in the hospital. The bond between them is so strong that Tenya decides to avenge his brother by seeking out Stain, the villain who ended Tensei's hero career. Tensei also has great respect for Tenya, calling him a "brilliant little brother" and apologizing to him for failing to live up to his expectations as his role model.
Later, during the joint training, Tensei shows a more positive and supportive attitude, which Tenya attributes to his brother's progressing recovery. After this, Tenya shows more determination to represent his brother, inheriting his hero name, Ingenium. In a flashback, some time after Tenya passed the Provisional Hero License Exam, Tensei is shown to be proud of his brother's progress and considers that he is ready for "tuning" his engines.
When they first meet, Tenya thinks that Izuku is an annoying person who can't keep silent in the entrance ceremony. He later reprimands him for making light of the prestige of U.A. High School, which earns Izuku mockery from the other exam participants. However, after observing him during the U.A. Entrance Exam, Tenya is greatly impressed by Izuku's heroic actions as he saves Ochaco Uraraka instead of focusing on himself in the test.
When they meet again, Tenya apologizes for his previous judgment of Izuku as he believes that Izuku had some kind of intuition that he himself lacked. Along with Ochaco, Tenya is one of the first people to befriend Izuku on their first day of school. Although he greatly respects and admires Izuku, he also views him as a rival; Tenya feels that he needs to challenge him in order to grow as a hero. However, the rivalry between them is much friendlier than Izuku's other rivalries. Tenya respects Izuku for his dedication towards a goal or task once he has put his mind to it and not giving up on said goal or task. Likewise, Izuku respects Tenya's leadership, determination, and perseverance.
Since they're both friends with Izuku, they become friends with each other too. Tenya and Ochaco both mutually care for each other's well-being and both express concern when the other is put in harm's way. The two seem to trust each other a great deal and work well together as a team, although they did find themselves on opposite sides during the U.A. Sports Festival's Cavalry Battle. During the Cavalry Battle, Tenya surprises Ochaco with Recipro Burst, with Ochaco playfully pestering Tenya afterwards for concealing his abilities which caused Tenya to profusely apologize.
Tenya, like most of Class 1-A, is also accustomed to Ochaco's usual cheery demeanor, and as such becomes somewhat unnerved by Ochaco's determination for the then upcoming Sports Festival. Tenya and Izuku are the only students Ochaco is comfortable sharing her reasons for wishing to become a hero with, and Tenya, like Izuku, believes that Ochaco's goal is a noble one. Tenya believes that there’s no shame in her quest for wealth, even before discovering it was only due to Ochaco's wish to improve her parent's lives.
Because of their equally forceful personalities and very different personal values, Katsuki and Tenya don't get along well. Katsuki looks down on Tenya's privileged background and dislikes being ordered around by him, whereas Tenya disapproves and frequently reprimands Katsuki for his improper behavior, questioning his intentions to become a hero. This is especially apparent when they’re forced to partner up for the Battle Trial.
Despite their bad standing, Tenya joins some of his classmates in saving Katsuki from the League of Villains. It is unknown what sort of standing they have now since this experience.
Tenya and Shoto get along well. At first, their relationship is only by mutual agreement, where they formed a team to advance in the U.A. Sports Festival. Later, during the tournament, Tenya loses against Shoto in their battle, although he does not bear a grudge as a result of it.
Their friendship begins to form during the Stain incident. Shoto realizes that Tenya is seeking revenge against the Hero Killer for severely injuring his older brother, Tensei. During the battle, Shoto calls out to Tenya with strong words to set him on the right path, and together with Izuku, they cooperate to defeat and arrest Stain. Later, Tenya thanks Shoto and Izuku and apologizes for his behavior.
Their relationship has improved over time. During the Joint Training Battle, before their match against the Class 1-B team, Tenya is the only one of their team who realized that something was bothering Shoto, which surprised his teammates, who wondered how he knew that Shoto had something on his mind considering Shoto's expression rarely changes.
After their match against the Class 1-B team ended in a draw, both students try to support each other.
The two are partnered up during the final exams against Power Loader. They’re shown to work and get along well. During the exam, the two show trust in each other as they use the combined power of their Quirks to throw Mashirao through the gate, resulting in the two passing.
Tenya is usually the first to chastise Minoru for being an unabashed pervert. Minoru, in turn, views Tenya as a killjoy and a prude.
His dislike for her escalated when she forgets and dismisses his name, also making him unwillingly use one of her inventions that he rejected. He openly voices his dislike of her to Power Loader. Mei simply does not seem to mind.
Pro Heroes 
Tenya ignores Manual's warnings against pursuing vengeance and is scolded for it after the incident. In the end, Tenya promises not to make the same mistake again, so they're not on bad terms..
Tenya despises Stain, the villain who severely injured his older brother Tensei. Tenya seeks out Stain in Hosu during his workplace experience and confronts him in a rage. Stain first regards Tenya as a child in a suit, then as a foolish example of the kind of false hero he was trying to purge. He scolds the young hero over his selfish desires of revenge over saving the Pro Hero he was about to kill.
Despite the fact that Tenya will never forgive him for what he did to his brother, he acknowledges that Stain was right about him and learns from his mistakes, resolving to start over as a hero. He also understands why some people start to admire Stain despite his criminal past.