We’ve seen various collaboration characters throughout the Neptunia series, and the latest to make it into Hyperdimension Neptunia Victory II is “Million Arthur-chan”. The official website has shared concept art for her.
As you might’ve guessed, Million Arthur-chan is a collaboration character based on Square Enix’s Kaku-San-Sei Million Arthur series. The official website indicates that another collaboration character will be revealed on May 21st, and also has third slot that’s just marked with “coming soon”.
Hyperdimension Neptunia Victory II is currently available in Japan for PlayStation 4.