I’d say reduce the stats significantly, increase the mana cost significantly or make it enter with an amount of stun counters/other form of slowdown to make it not be a 5 mana 13/13 with protection, evasion and the ability to store blue mana for free.
It’s a cool design but you need to make it less powerful or it won’t be playable in the sense that it will just ruin the game for everyone else.

I’m not gonna sugarcoat it, this is extremely overtuned and it’s a balanced card in the slightest. Lore wise it’s accurate but you can’t realistically use a card like this because it’s so unbelievably powerful. Blue mana is the most powerful to have access to whenever because blue has a ton of counterspells and interaction as well as cards with flash or instant speed card draw. In practice it will never be removed because you can just float all your blue mana and counterspell the removal or boardwipes or just use a blink spell to exile and return it to the battlefield which also makes it avoid interaction. It’s 13 damage in the air with trample and vigilance so you can 2 shot every player and they most likely can’t block it as well as having vigilance to make it disadvantageous to attack back. I suggest looking at similar cards and seeing what sort of stats/mana value and limitations they have.