I'm pretty sure it's just referring back to how they said the Demon Lord was already reincarnated before..
໒( ⊡ _ ⊡ )७
So I assume this is their discrete way of saying that he imbued his soul in that armor and gets new bodies that way...
( ＿ ＿)ノ maybe.
Just a Guess!!(⌒▽⌒)
from what i remember they use the constellation technique for reincarnation, it transfers the soul from the old body to the new one so it doesn't involve the armor( and new body is a baby, thats the reason why I said he cant just tranfer now, cant be a toddler for the story) . but i would prefer your theorie, it would make more sense !
Spoiler!
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In the near future they have to set aside their difference to beat their common and greatest enemy which is the emperor that killed them both and them ending up reincarnating. Yup the 2 girls the violet haired and orange haired girl are both going to be his wives. I just came back to check how will they draw the father's death so yeah.
so at this point the demon lord is just a flying sternum in an armour , the rest of is body including the head id destroyed and somehow he is still alive and going to recover from that ??!! he's not changing body and not yet at the level where he as multiple lives (fate soul) . damn they have good medecine regrowing limbs !! I guess I would be less bothered if he at least still had a head , you know ?