Izuku and Mirio meet by surprise before introducing the Gandes to Class 1-A, Izuku freaks out at Mirio's presence while Mirio just smiles at him and leaves. Izuku is reunited when the Big Three appear before Class 1.A and Izuku is impressed by Mirio's fighting skills.
After the surprise first impression, Mirio accepts Izuku to take his internships at the agency of his teacher, Sir Nighteye, who was once All Might's old assistant. All Might reveals to Izuku who Mirio is in U.A. and its fundamental role before they knew it: To be the original successor of the Symbol of Peace.
The relationship between Mirio and Izuku in the Academy and the Agency is that of Senpai-Kōhai, which in a short time, became stronger after adversity. During the Internships, Izuku and Mirio meet a girl named Eri with a rare and powerful quirk, who is the victim of a yakuza organization. The rescue of Eri and the destruction of the yakuza organization will be planned by several agencies of heroes with the support of the police, among the many agencies is that of Sir Nighteye with Izuku and Mirio as protagonists of the mission.
The mission turns out to be a bittersweet victory for the heroes because, despite the fact that the yakuzas are defeated and Eri is rescued, Sir Nighteye ends up mortally wounded and Mirio loses his quirk because he becomes the victim of a bullet that destroys the quirk. But despite everything that happened, Mirio maintains his trust in Izuku, despite the latter telling him repeatedly his desire to transfer the One for All to him and receiving a simple "No, Thank you" from Mirio.
MiriDeku is a rather middle-known, but well-received ship in the My Hero Academia fandom. Since Izuku and Mirio are like brothers to Eri, MiriDeku shippers often headcanon Mirio and Izuku dating each other, while raising Eri together. However, MiriDeku is overshadowed by many Izuku ships, and MiriTama for Mirio. Izuku's more popular ships being, BakuDeku, IzuOcha, and TodoDeku. Nonetheless, MiriDeku still managed to get a good amount of shippers, mostly due to the friendship that the developed with each other in season 4. On AO3, the ship has 250+ fanfictions.
- Izuku's Relationship with Mirio on the My Hero Academia Wiki
- Mirio's Relationship with Izuku on the My Hero Academia Wiki
- Both, Mirio and Izuku have shown themselves to be All Might fans from a very young age.
- Mirio was the candidate to inherit the One For All before All Might meets Izuku.
- Izuku was horrified when he learned that Mirio had lost his Quirk.
- Mirio and Izuku are often seen close to Eri.