Hyperdimension Neptunia OVA

The four goddesses alongside their sisters—Nepgear, Uni, Rom, and Ram—meet at a famous mountain resort in Lastation Kingdom seeking that nostalgic "summer vacation" feeling. But their plan to sit back and relax in a hot spring is interrupted when the younger sisters are swept into a portal leading to a parallel universe! The seemingly unfortunate situation takes a comical turn when they are greeted by a familiar face.

(Source: MAL)