Fairy Tail vs Final Fantasy XV
Connection:
Both are the one of the main antagonists of their series who are immortal masters of forbidden and unhallowed magics with demonic origins (Zeref is a master of Death Magic and has created multiple demons throughout his lifetime whereas Ardyn became a host to so many daemons that it warped and corrupted his body and soul), who're nigh unkillable, and the true masterminds behind most of the conflicts in their universes
Both are secret relatives of the main protagonist (Natsu is Zeref's brother, whereas Ardyn's brother Somnus is Noctis' ancestor), who're fully aware of and manipulating the main protagonist into the position wherein they can finally kill them to fulfil their plan
Both their plans also involve creating an evil superpowered empire that they're the true power behind (Alvarez Empire and Niflheim respectively)
