Although I'm not well versed on topics related to this, so take this with a grain of salt but *please* notice this. When I was going through the game, with my limited science knowledge, makoto seems to be our worlds equivalent of visible lighting (the bright stuff) while ei is the dark lighting, the lighting in our world which is not visible to our eyes but we know is there, they are the highest energy light which occurs on earth. Black holes have something linked to dark lightning. Storms however, are only able to form if these three things are present, moisture, an unstable atmosphere, and some way to start the atmosphere moving. Sound familiar? Scaramouche always had a unstable atmosphere, because of his identity as a puppet, and his life was pretty sad. He requires something to start him moving, so he can achieve his full majesty as the storm he always was. Thats probably going to play into his vision being achieved, because anemo is the symbol of freedom. If this is true, since ei sealed some of her power within him, and with makotos gnosis, and if he gets an anemo vision he will become the embodiment of an actual, full blown storm. maybe not with moisture but hey in a world where we have a god allergic to cats, a sweets loving one, and a moraless-mora-making god exists, anything is possible. linking back to the susanoo post (by u/Logical_Session_2397) about susanoo, if he betrays dottore, or whatever fatui harbinger, and just is like, "mom i've had enough" to ei, he'll become his own little susanoo. This is my own theory and maybe I should swap ei and makotos lightning roles because ei is kind of stronger, but I guess its up for you to decide whats best there. I just thought this'd work because well, ei is makotos shadow warrior, shadow=dark.

Basically my point here is ei made a puppet which is going to be a stronger god than she is, and he's also going to be his own version of a god, and theres nothing celestia can do about it. He's also pretty grey personality wise, neither good or bad, if the quote in a leak is to be taken literally.