One-Punch Man is currently in a flux with fans. The second season of the series did not quite live up to the expectations built up after the impressive debut of the first season, and time's not exactly being too kind either as fans are continuing to find impressive little details snuck into that first season. Along with the many humorous sight gags littered throughout the first season, there was actually a pretty heartwarming bit of foreshadowing for everyone's favorite bicycle riding hero, Mumen Rider.
As shared by The GirlNamedJurassic1 on Reddit, Mumen Rider manages to save a young boy's balloon from floating away in Episode 4 of the series, and it appears that this bit of heroism had such a strong impact that the same boy was the first one to cheer on Mumen Ride against the Deep Sea King in Episode 9.
The first season of the series ends up better compared than the first for a lot of reasons, but one of the ones that sticks out when looking at details like this is how Mumen Rider is depicted. Like this Easter Egg suggests, Mumen Rider actually has a pretty strong character arc in the first season. Fans see how the humble hero ends up becoming larger than life as he stands up to the Sea King, and the series builds a lot of tension from this.
Because Mumen Rider becomes this heroic figure tragically standing up against unbeatable odds, there's a great sigh of relief when Saitama arrives. Saitama's used as a plot device in the second season as well, but it carried more significance with this fight in particular. Fans were rooting for Mumen Rider here, and didn't root for him in the same way as say, watching him get quickly pummeled by Garou in Season 2.
But fans can currently check out One-Punch Man's first two seasons on Hulu and compare the two Mumen Riders for themselves! The second season of the series ran for 12 episodes earlier this year, and is directed by Chikara Sakurai (Naruto Shippuden episode director) for new production studio J.C. Staff. Viz Media has licensed the season for an English release, and they describes One-Punch Man Season 2 as such:
"Saitama is a hero who only became a hero for fun. After three years of "special training," he's become so strong that he's practically invincible. In fact, he's too strong—even his mightiest opponents are taken out with a single punch. Now, the great seer Madame Shibabawa's prediction about the Earth being doomed seems to be coming true as the frequency of monster incidents escalates. Alongside Genos, his faithful disciple, Saitama begins his official hero duties as a member of the Hero Association, while Garou, a man utterly fascinated by monsters, makes his appearance."