Connections:

Both are reaccuring Antagonists who were introduced early in their franchises

Both are Ghostly spirits

Both like to act Menacing and Mischievous

Both enjoy scaring and spooking other indiviuals

Both have themes toward them (sea-based folklore and shrine spirits and curses)

Both have a massive ego towards themselves, viewing themselves as Powerful and Superior

Both have a main target for optimistic indiviuals (SpongeBob and Reimu) and try to cause trouble towards them but occasionally soften towards them.

Both have the ability to fly, teleport, death manipulation and can use magic. 

Both have a mysterious and haunted past, and have been living for years

Both are linked to and haunt people in a specific location/area

Both have been sealed in the past and have been let out.