When a story/game/etc. has a character named Zagreus with the title “Prince of the Underworld”, and Melinoë with the title “Princess of the Underworld”, is this story a derivative of the Hades I & II games? Note that both Zagreus and Melinoë aren’t original creations of these games. They are from mythology & folklore, but they barely appear in ancient documents (Zagreus is basically just a name in ancient myths, and Melinoe only appears in a few Orphic Hymns)
As with every legal question, it depends on the country you’re in. And in those kinds of cases maybe, how good a lawyer you can afford can be more important than the actual law. You can be completely right and still be bankrupted by legal costs if you plan to go up against rich companies and/or people.