In canon Tetsutetsu and Kendo are first shown as classmates in the second season. The only interaction indirectly shown was Kendo giving up her spot to be in the tournament over to Tetsutetsu’s team because “They fought until the end.” Tetsutetsu seems to appreciate this gesture. Kendo cheers for Tetsutetsu during the tournament.
Although these characters pop up through out the show in season 2 they aren’t seen interacting again till season 3. When the Vanguard Action Squad attacks the Summer Camp in an attempt to kidnap Katsuki Bakugou. The two were together during the “Test of a Courage.” Where 1-B are the scarers of 1–A. They are together when Mustard’s poison gas surrounds the part of forest there in and effectively takes out some of their classmates.
Later on they give their passed out classmates to Yui Kodai to look over while they find the source of the gas. Thanks to gas masks made by Momo Yaoyorozu they are able to travel further into the gas without being poisoned. When they have gone slighty further into the gas Kendo stops Tetsutetsu to warn him about the gas. Tetsutetsu tells her that he understands it’s dangerous and that she should give him credit. Kendo undeterred points out that it gets thicker towards the center of the forest and that the person who has the poison gas quirk must be in that area. She also warns him that they can go further thanks to the masks but they can only filter so much and that it could be risky. Tetsutetsu takes this into consideration before taking off saying “So all we need to punch the guy responsible for this!” Kendo follows him and smiles seemingly to have a quiet admiration about Tetsutetsu.
Once they reach the center Tetsutetsu rushes in only to get shot by Mustard. Thankfully his steel quirk protects him from further damage but his gas mask comes off in the process. His steel is weakened by having to hold his breath to keep from inhaling the poison gas. This continues with Mustard shooting Tetsutetsu as his steel weakens. It even comes to Tetsutetsu having to save Kendo from a bullet but his steel is so weak that the shot draws blood. Kendo eventually steps in and with her enlarged hands and starts waving them around to move the gas around so that Mustard can’t predict her movements. She lectures Mustard on his beliefs while Tetsutetsu takes this chance and punches Mustard effectively knocking him out. After defeating the Villain, Itsuka is seen holding Tetsutetsu and Mustard with her hands.
Once again these characters show up but aren‘t shown interacting till season 4 during the cultural festival. Where Tetsutetsu says Kendo looks good in her dress that she is wearing for the beauty pageant and when the contest begins, Tetsutetsu is seen looking at Itsuka next to Eijiro Kirishima.
When the Itsuka team's match against Momo Yaoyorozu's team begins during the joint training arc in Season 5, Hanta Sero asks Tetsutetsu what is Itsuka's role in Class 1-B, Tetsutetsu responds by shouting that if it weren't for her the Class 1-B would fall under the influence of Monoma and calls her the older sister of Class B. Tetsutetsu is constantly shown cheering for Itsuka amongst the students and when he wins he smiles and ends up saying “That’s our Kendo!”
Since these characters are background characters they aren’t too popular, so their ships wouldn’t be either but this ship has become mildly popular in the fandom since people love their dynamic and think of it as a cute ship. This ship gained considerable attention during season 2.
The majority of the fandom sees this as Tetsutetsu has a crush on Kendo but doesn’t believe someone as smart and pretty as her would ever like him. Or the other way around that Kendo believes Tetsutetsu isn’t interested in her when really he is also in love with her.
- Itsuka's relationship with Tetsutetsu on My Hero Academia Wikia
- Tetsutetsu's relationship with Itsuka on My Hero Academia Wikia