TodoDeku

TodoDeku is the slash ship between Shoto Todoroki and Izuku Midoriya (Deku) from the anime and manga series My Hero Academia. The anime they belong in is shounen, so it is extremely unlikely that TodoDeku would be canon, especially considering that one of the characters may become canonically involved with another, Izuku Midoriya at Ochako Uraraka. Even so, it is an extremely popular My Hero Academia ship and probably the most popular slash ship of the series.

Canon (SPOILERS FOR ANIME)
In the currently available anime so far, Shoto began an arch-rivalry with Izuku during the U.A. Sports Festival arc, claiming he would beat him using only his side that controls ice. The reason for this was because he did not want to use what he felt was his father's power, and wanted to prove to his father- Endeavor- wrong in that he wouldn't win with only the power received from his mother. Although in a rivalry, Izuku still admired and respected him, admitting that Shoto was far stronger than him.

One of the most important things in this series revolving them is that in their fight in the festival changed Shoto's ways and opened him up to massive character development. It is revealed that Shoto's past involved abuse and overworking, with even his mother being driven madly to scarring his eye with boiling hot water. After this, his mother was sent to the mental hospital by Endeavor.

Izuku was the breaking point that helped Shoto embrace himself, not by making him give into his father's will, but by making him realize that the connection between the quirks of a person and their parents are not what matters most, but being able to recognize it as the quirk that they as a person have. One of the most iconic lines stem from this scene, "It's your power, isn't it?!" said by Izuku. Izuku helping him during the fight, even knowing that Shoto was only using half his power and would most likely beat him when accepting his firey side, was a sign that Izuku cared much more about helping others- including Shoto- than winning.

Because of this fight, Shoto had accomplished character development in many areas. In the Vs. Hero Killer arc, Izuku was stuck in a bind while attempting to save Tenya Iida from "Hero Killer" Stain. This caused him to secretly send out a signal to his location on his phone, which Shoto- although hesitantly, questioning whether he would really be in trouble- was the first one to comply and come to his area.

An example of character development was that near the end of season 2 of the anime, Shoto became angry on behalf of him and his friends Tenya and Izuku for having trouble against the law despite the fact they stopped a serial killer. This shows that Shoto is slowly but very surely opening himself up to others, which is a huge thanks to Izuku's help.