Mega Man creator Keiji Inafune’s appeared in Hyperdimension Neptunia mk2 as a guest summon character. He’s helping Idea Factory design a theme park for Bakudan Handan and he might be working on Compile Heart on Overwhelming Game Infinite Souls too.
A retail listing notes Keiji Inafune is participating as a guest character designer. What isn’t clear is if HMV is talking about Keiji Inafune from Comcept or "new" Keiji Inafune, the game’s director. Usually, "new" Keiji Inafune has the character for new in front of his name so the two Keiji Inafunes may be working together.
Disgaea artist Takehito Harada is the main character designer for Infinite Souls. (You can see screenshots of the game here.)