@EnkryptionAlright so
Overall, the concept is...mhm,
fine. A weak demon that was about to be sealed, begged to work for the maids instead.
That said, there's a number of things in this idea that don't really work.
Lets start with the classifications. Perhaps I could have explained this better, but anything below 'High Demon' level is often little more than an animal. Demon Beasts are basically the animals of the demon realms. Little intelligence, but can be tamed by demons or summoned by particularly powerful mages. Whelps, are going to be even weaker with even less intelligence and sentience. They're basically krill, plankton, small slugs you find on the underside of a rock. Such beasts aren't worth sealing because they are far too numerous. It'd be like trying to cage every animal on five different earths if they did it. Easier to just kill them and let their souls return to Naraheim or purify them rather easily with a holy weapon.
Not that they can't get powerful - that's why and how Devil Beasts exists. Such creatures that lived for awhile and were able to essentially self-evolve.
Basically, she needs to be a High Demon.
Now, secondly, blood demons if I had to describe them are the embodiment of Lust, Wrath, Slothfulness and Greed. Basically every single negative human emotion wrapped up into one tightly wound choleric, irritable and angry bundle. That is to say, there is not a single blood demon that would be cowardly. Its basically hardcoded into their entire being to be violent murder happy human-eating psychos. You want a demon that is cowardly and shy, or at least appears to be - those would be your Tear Demons. These demons would happily fight to their own death just to prove a point even if they knew they were likely to get beaten to a bloody pulp unless the power difference were just too great. Like say, a High Demon trying to fight a Primarch. Not a single high demon would dare.
Thirdly, Blood Demons magic is entirely destructive. It Explodes, burns, slices, cuts, destroys, vaporizes, etc. It can take many forms - such as these bloody butterflies, but as it stands I'm gonna need more info on what it does if I'm to approve it for the previous reasons as it needs to embody 'pure and unfiltered violence and destruction' in some way. Perhaps her blood itself is the weapon and its extremely corrosive or toxic. Perhaps her blood just causes things to rot.
Lastly, a minor thing is and perhaps I also left it open to too much interpretation is that blood demons tend to be Animalistic in appearance. That is to say, vertebrates. Wolves, bears, elephants, cats, dogs, lions, tigers, penguins, birds. Something like a Butterfly would be better suited as an Eye Demon, as they are specifically noted to be insectoid in appearance.
I think a good bit of the problems could be dealt with if she was an Eye Demon. They would have no qualms about fleeing instead of fighting to preserve their life, and a butterfly would fit here better. You'd just need to change her abilities a bit to fit in line with the Eye Demons lust and penchant for magic and knowledge.
