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I would refrain from using any kind of traditional FF summon that isn't in game yet. There are a number of reasons for this. There's no evidence of their existence in the ARR universe. You'd need to make your own "fanon", which will become invalid as soon as Squeenix decides to introduce official lore. If they do that, then whatever you write has a big chance of becoming completely invalid, canon-wise.
If the creature is in game, however, and you can find evidence of their summoning in game then feel free to use it. For example, voidsents and golems are constantly summoned or created by enemies, so we can safely assume that they are things you can summon. From there you can infer other types of creatures that could be summoned, but the key is that such a thing must be grounded in some in-game creature.
What I'd do: First, search for a creature thematically or physically similar to Anima. If there's one, go to step two. Adapt that creature into being Anima-like.
Otherwise, you'll have to adapt Anima into being something else. Not a summon in the sense ARR's summoners use it (so it's not the essence of a Primal), but it could be some other type of creature. Maybe a type of voidsent or a golem.
If the creature is in game, however, and you can find evidence of their summoning in game then feel free to use it. For example, voidsents and golems are constantly summoned or created by enemies, so we can safely assume that they are things you can summon. From there you can infer other types of creatures that could be summoned, but the key is that such a thing must be grounded in some in-game creature.
What I'd do: First, search for a creature thematically or physically similar to Anima. If there's one, go to step two. Adapt that creature into being Anima-like.
Otherwise, you'll have to adapt Anima into being something else. Not a summon in the sense ARR's summoners use it (so it's not the essence of a Primal), but it could be some other type of creature. Maybe a type of voidsent or a golem.