This episode does not really continue from where the main story left off, no big surprise there. Actually, I am not really sure where on the timeline this episode would fall. It seems to fall afterwards based on the fact that no one is even mentioning killing her for real and some other little conversations. On the other hand, they are still with the teacher and the teacher mentions he wants them to all graduate, so it would seem it's before the main story ends. I just decided it's a stand alone and doesn't actually fit in the main story timeline at all.
As for what it's about, it's a game where they all get fake weapons and are trying to steal a pin off the main characters bathing suit before the sun sets. It kinda seems like a parody of the second hunger games, total drama island, btoom, etc. It's a good laugh although it kinda confused me about some of the relationships. I really would like to know where all that was going.
Anyway, it's a good watch. If you have watched the series, go ahead and watch this too. If you haven't watched the series yet, you probably should. If you don't, you just won't get as many of the jokes. It's a lot more light hearted than the series though.
I'd say this anime is mildly interesting. I loved the actual Riddle Story of Devil so much, i couldn't enjoy this much without thinking about the real show. In fact, it's the real show that makes this mildly interesting. It doesn't have anything to do with Riddle Story of Devil other then the fact it shares the same characters and the target is still Ichinose.
The story doesn't have any death drive. It's more of a fun vacation type theme. The characters play a little game in which they have to take a pin off each others swimsuits. It's visually more explicit then the actual show, and full of more humor.
Don't watch if you're expecting something great. Watch it if you have a minute and could use a good laugh and reminice.