(Note: I don't know if this has already been done before, but let me know if it has so I can give the original credit to whoever made this first, and put it as a revision, and as always if I left out any info that needs aswering, I'll make sure to edit it and revise it when I have the chance.)
A Sapper, or more commonly referred to as an Absorber in some cases, is a type of Mamono that, unlike the common Succubus, cannot alter her features freely. They are essentially demonized assimilators, driven by the need to become better than they already are. Since they can't shape themselves without first absorbing bits and pieces of other mamono's endowments to begin with, they go out and attempt to find other mamono, one of their goals mainly trying to shape their original form to suit a man's tastes. They can also absorb abilities owned by other mamono, however depending on how much of the body part or ability they want to absorb it may take longer, making time a key factor when the mamono in general prefer to keep all their parts and pieces intact. For example, an Ifrit's natural ability to create fire would take a little over twenty minutes to assimilate fully. Higher classes of mamono take longer for their features and abilites to be absorbed into the Sapper. Because of this ability to take in, their measurements haven't been accurately taken, but it's believed that all Sappers start out as flat as an ironing board until processing more and more from other female beings.
They are a race that is quite obsessed with all the possibilities with what they can absorb, and certain individuals who have a high amount of any one thing are highly hunted by Sappers. They can be greedy in some cases, but at the same time they also know that having too much can be a burden as well but the amounts that Sappers want to take in varies by individual. Despite wanting to assimilate other traits of various species of monster girls, they can also be content at being the best at one thing, such as being a practical devoter to fire, or being the most muscular girl in the world, and so on and so forth. Also, while the Sapper species of Succubi does take parts/abilites for herself, she is more than willing to patt with some and bestow it upon another Mamono, provided the monster girl in question is on good terms with the individual Sapper. Sonetimes when retiring from having a 'best in the (insert whatever it is the Sapper wants to be good at)', coming of age or whatever reason there is for the Sapper has for doing this, she will give it all away since the afterlife has no place for her collection during the span of her life. That and it's possible a Sapper feels that what she got in life must remain in the mortal plane of existance.
They also have a limit to what they can actually absorb. While a Sapper can take in numerous traits and abilitied, they can't take a zombie's undying ability, a slime's liquid solidarity, immortality in general (although her aging can be delayed by absorbing another's life force by a minimal amount, if the individual feels the need to live a long life), abilities and looks other Succubi of their family have, and the Pharoh mamono's ability to command her followers to do her bidding in an enthralling fashion (but she can assimilate an ability that counteracts this effect). What a Sapper can absorb is, again, numerous, however an idea can be gathered from these few examples: Muscle Mass, Breast Englargement, Butt Expansion. Size change, Magical Mastery over elements and magic in itself, Knowledge, Underwater Breathing, Tooth shape, Eye&Hair color, and Weight Gain (although knowing the sensual tastes of the average human being, most Sappers will probably detest this.)
When hunting for a husband, they do it in a fashion similar to how a Succubus usually would: in a verypresentable manner. By this time a Sapper will have all the necessary traits needed to win over her beloved other. However, a Sapper does not have the natural seductive pheromones all Succubi have, so either they go the normal route of trying to won his heart with the features acquired over time, gain an aphrodisiac ability to ease the process of getting a human male as a husband, or gaing more features so that way the next time she comes around the man will be unable to resist. Men who are married to these individuals find that most of their fantasies are mostly fulfilled as the Sapper can assimilate forms such as having a Centauric lower body, having the look of a Minotaur girl, and even taking on the appearance of a Chimera (a plus being that there is only one personality in that body). Moreover, they can't assume the forms of the other members of the Succubus family despite having relations to them, as well as being unable to turn slimy like what most slime monster girls are.
Another downside, beside what wad mentioned before, is that Sappers require physical contact in order to for the assimilation process to work. If a Sapper wants the power over fire, for example, first she meeds to absorb a fire-resistant trait from another mamono who's preferably not on fire to begin with before moving on to aquire the more powerful ability.
They naturally blend in with the human populace, since it is quite hard to distinguish them due to Sappers being born with almost none of the usual Succubus features. There are no horns, no spaded tails, and no clearly visible wings. In fact, if it weren't for the more lustful desires to take from others as well as their need for a husband, telling them apart from ordinary human women would have been next to near difficult. And since they are born with pretty much a human appearance, they are able to slip past checkpoints where guards of the Order scan them for signs of having a falsified form, bypassing most forms of security save for spells that check for signs of demonic energy in people.
The amount of Demonic energy a single Sapper originally has is very minimal to begin with. However, as more and more is taken from other species, races or otherwise (without harm or pain, or even death), they can hold massive amounts of demonic energy which by then replenishes quickly over tine.
Physically, without any additions to ther arsenal at the beginning, most Sappers can hold their own, although this is in comparison to the avetage human being. While it is true that Sappers are Succubi, they are inferior to all other members of the family tree at the start of the collective hoarding. Mentally, the Sappers have nearly equal IQ as an average hunan being. It should also be of note that while Sappers do share differences with the other Succubi races, one detail goes into their aging , as even elder Sappers look as if they are in their mature adult years, retaining the youthful beauty that entranced theur husband at the start of their marriage.
A single Sapper, despite not being well known throughout the world, is highly regareded as a dangerous type of Succubi by the Order, given how she can be quite fearsome over time. As a result, they are cautious and wary although all of them are driven to compkete their life goals and finding a suitible mate.
Also, it is impossible for any Sapper to be stronger than the Demon Lord, or any god for that matter, since the amount of time needed to aquire that much power would take eons, and by then the Sapper(s) would have passed on. This is because they can only delay the aging process, the oldest recorded Sapper being nearly two-hundred and ten years old. Even though they were more than capable as a species to overthrow the Demon Lord, the current ruler took notice of this and made limiters so that way her rule would remain unchallenged due to the nature of this race of Succubi.
(Pretty much finished, let me know if there are any gaps of information I need to fill in.)