BlazBlue vs Fate/Grand Order

Connection:

Both are individuals who were once good people but were forcefully controlled by higher powers (Terumi being the soul of the Susano'o unit which gained freedom of it with it then inhabiting the body of a young man with green hair and The Grand Caster having nested inside the corpse of King Solomon for a long time, and being the aggregate form of the seventy-two Demon Gods)

Both view humanity as beneath them and want to destroy everyone and everything in order to make a brand new universe that doesn't have to suffer by the rules that were pre-set (Terumi longing for freedom and to be free from the endless cycle of him destroying everything that Amaterasu would create so he could be his own individual and Goetia not being able to accept such contradictions and unfaithfulness, and set out on a quest of self-reform in order to reset the objective of serving humans and to become the sole existence in this planet; in other words, the beginning of the great venture of becoming God)

Both have a higher form that came into existence because of the defeat of one of the characters (Terumi finally reviving his body as Susano'o by using the Hihiirokane to shatter Hakumen's soul and after his Grand Caster form is defeated once again, impressed with the heroes resilience, decides to remove his disguise and reveal his true identity as Beast I, Goetia)

Then right before they went into their final fight, they got much more powerful (Susano'o absorbing Noel, becoming immune to Phenomenon Intervention and Goetia gained a very limited lifespan and became able to comprehend humans, something that until that point he was unable to do, finally reaching the state of a wise "human king" to surpass even the real King Solomon)

However, in the end, both got fully erased from existence (Susano'o fought against both Ragna and Jin Kisaragi, with the former removing his Idea Engine's limiter and eventually managing to rip Terumi out of the Unit, and with the latter perceiving the God using Order. Terumi was dragged into the Gate and was killed by Ragna, thus ending the life of a God. Goetia meanwhile decided to use the remainder of his existence to kill Ritsuka despite knowing that the act is meaningless. After this final confrontation, Goetia contently vanishes, stating that the briefness of human life is surprisingly interesting)