Yes, it is a sequel that seemingly takes place during either a vacation period or school trip, not sure which because the English is machined until such time, if it happens, as Illusion releases this on Steam.
There might be fewer community creators playing this game or using the studio, which is understandable, aside from some slight art updates and the topic system, it is basically Koikatsu on an island instead of in a school. They could have made this into a DLC for the original it is so similar.