[Kurona]

That is what I'm thinking too. They've shown off Boost Magnum at Tamashii Nations and they highlight the form-swapping gimmick in the tweet that shows these two; so I imagine it'll be a release of Boost Magnum with the Fever buckle, scarf and eyes. I think that makes the most sense! But I'd hope it comes with duplicates of the Fever parts so you can at least have both Fevers displayed at once -- or thinking backwards, something to do with the spare full figure you'd be left with