In Chapter 19, Izuku accidentally slips and calls Inko "mom" for the first time, causing her to burst into tears and hugs him.
Later on in the same chapter, after a full day at the amusement park, it finally hits Izuku that he not only had friends, but friends that cared about him so much that they brought him to an amusement park just to see him smile, causing him to burst into tears himself.
Even though Izuku has such a Dark and Troubled Past and is marked by physical and psychological scars, his classmates go out of their way to show him nothing but support and acceptance from the moment they meet him - everything from making increasingly implausible excuses to cover up his bringing a cat to the first day of hero school; to bringing him to an amusement park just to make him smile when they realize they've never seen him smile before; to searching for him when he runs away from home in the middle of a rainstorm with a fever, bringing him back out of the rain and home to his mother, and huddling around him while enduring the sensory deprivation of his uncontrolled Quirk just so he won't be alone when he's A Friend in Need.
When first moving into the dorms, Izuku is discovered to be painting his room. Soon, all the other students take over and add something to the walls and floor.
Yaoyorozu, after hearing that Izuku loves stars draws him and entire galaxy in the ceiling in glow-in-the-dark paint.
When noticing Izuku’s being overwhelmed by everyone painting his walls, Todoroki takes Izuku back to his room. There, they unpack the last of Todoroki’s possessions he brought and, after Izuku stumbles across Todoroki’s skates, do some indoor ice skating, which leads to Izuku’s third smile.
We don’t actually get to see it, but Eri plays with Cat and says she likes the name after Izuku rescues her from Overhaul.
, Izuku accidentally slips and calls Inko "mom" for the first time, causing her to burst into tears and hugs him.