The beach episode is such a common anime trope it's practically synonymous with the medium itself. It doesn't matter what the genre is, ratings go up when there's fan service, and what better way to shoehorn some in than by setting up a situation where everyone barely has clothes on? While this might be pointless for a show like High School DxD, where everyone is scantily-clad all the time anyway, in other shows the beach is only logical way to throw in some fan service.
While the beach episodes of anime sometimes move the plot along, more often than not, they come completely out of nowhere. The anime characters at the beach might be having a good time, but they're not necessarily doing anything particularly noteworthy from a plot or character development standpoint. Sometimes, you have to wonder if there was any reason to include the episode besides fan service. Here are some of the most inexplicable instances where your favorite characters got all sandy.
This episode feels like it really came out of nowhere, specifically because it takes place in the middle of a major arc. Yes, watching Orihime learn how to use her breasts as a bucket is entertaining, if a bit weird, but viewers who are invested in the main storyline may want to see it, you know, actually get resolved. Save it for the filler arc, okay guys?
High School of the Dead is an anime about a group of kids struggling to survive a zombie outbreak. In an OVA titled Drifters of the Dead, the gang winds up on a deserted island, and uses the opportunity for out-of-nowhere beach time fun, complete with hallucination-induced make out sessions. It's utterly bizarre.
Higurashi no Naku Koro ni is a profoundly disturbing series about a village-wide conspiracy and an imaginary psychiatric condition that causes people to do terrible things. So, not exactly a sunny premise. The episode where the main characters go to the beach and splash around in cute swimsuits, therefore, is utterly incongruous with the brutality of the rest of the series.
Team Natsu is supposed to be training for the upcoming Grand Magic Games. Somehow, they end up completely distracted from their original goal, and spend the whole episode playing around in their bathing suits. Considering the big deal the team made over needing to start training immediately, the whole beach episode thing was more than a little surprising.