ハッピーシンセサイザ

AND YES GUMI HITS TOP NICO NICO CHARTS AGAIN (alongside Luka)~

As the producer's name suggests, its easy-pop style, with a more or less "calm yet hopping"... well, at least something that would make for good "this is the last episode and we're showing the result of what everyone is doing after the big finale has ended.

...

So the title is "Happy Shoe Size", I think, which means... they're pretty happy about shoe sizes. :V

EDIT: So it turns out the actual name is Happy Synthesizer. But seriously, Happy Shoe Size would have been such a better name :V