Chest plates aren’t meant to be flat. They’re meant to be round. The reason is that rounded armor is structurally more stable and it’s easier to get a weapon to deflect off rounded armor than a flat armor. There should be plenty of space for breasts in regular medieval armor without needing any sort of modification.

Having the chest plate fit the breasts actually introduces a point of weakness, since glancing blows will be deflected toward the heart.

The problem with boob plate is how it deflects attacks. There are plenty of places on that armor where a spear jab would deflect upwards toward the neck area.

Flat isn’t really what you want either for these. When the weapon deflects and slides off to a side, that steals a lot of the energy from the impact. If the weapon strikes a flat armor, it would be much more likely to damage the armor. That might mean caving in the plate, or fully piercing it. Neither is great. (And even if the armor withstands the hit, it might knock you on your ass, which could very well be a death sentence)

There’s usually some room in these sorts of armors. unless you’re tiddy is comically big, I’m skeptical that you’d need a great deal of accommodation. But even if you do, the armor shouldn’t look like booba from the outside.

Something like this should presumably work, but I’ll admit I’ve never had boobs inside of a suit of armor.

Yea Plate Armour leaves place at the breasts anyways. As long as she does not have literal melon sized boobs they would fit comfortably.

But then there are a lot of historical breast plates with abs and big muscles so it’s not improbable that she just wants to express herself.

1, the demon is wearing armor but not on their body. Deciding that their extremities are of need of armor but not their core is a pretty half assed worldbuilding excuse to make a hot demon character who shows off her boobs even though it’s unlikely to be practical for combat

With respect to number 2 I assume they’re talking about the detail added to the top of the breastplate to imply the boobs, and the sculpted shape where you can see the boobs separately, not the fact that there’s enough room for boobs. And sculpted boob shaped breastplates are generally not super effective as you want a shape that swords or other weapons glance off of, unlike concavities between the breasts which would guide weapons to a point where force could be concentrated.

3, I assume that’s mostly so it can fit in the composition, or is easier to draw without overlapping the raised arms, but yeah it’s a bit odd

I think it’s perfectly fine to like fantasy stuff with loose world-building and costume design based on whatever is cool or fun or hot, but it’s just as valid for folks like the person who made this to want costume design that’s grounded and doesn’t exclusively sexualize every female character

3. I know butt wings are a thing in some Japanese works, it’s mostly for fanservice as best I can tell. I don’t know where or when the concept originated.

I think the positioning of the wings is more towards the center of mass for a humanoid with heavy legs

Tell that to a Roman soldier in their mini skirts.