As a class-4 Pureblood, a Darkside is the pinnacle of what a 'natural' Heartless is. Awe-inspiring in their power, they are one of the few Heartless that never leave the Shard of Darkness to do anything but obtain a husband for themselves, and for the most part, they don't even directly enter into the material plane to do just that.
A large muscled 25-ft woman stares up off into the distance with her gleaming yellow eyes. Her skin a pale-white is only visible for portions of her face and torso. As a black shadowy scarf-like object covers her mouth. In-truth this scarf object are actually tentacles stemming from her head. Where her should be are many large and waving black tentacles that move about from her will, such tentacles can mimic hair-styles if she wishes to do so, but for the most part they wave uselessly in the breeze. It legs and arms are completely inky-black, and utterly massive due to her size, her hands are five-fingered claws and her feet possess no digits, are incredibly thin and curl upwards. Two twisted small wings can be seen on her back, far too small to even imagine of gliding, no less flight. Her most distinguishing feature isn't her rather large breasts covered in shadow, but rather the heart-shaped hole at the top part of her stomach, just barely above her belly-button. She can use her innate magic to shrink herself to 7ft at-least, causing the hole to shrink also and not be as distracting.
Darksides are an interesting Heartless mamono, as they're one of the few that rarely if ever ventures out of the Shard of Darkness realm. Darksides serve as, essentially, leaders among the Heartless mamono hordes that reside within the spirit realm. They have no obligations to do so, but they're among the oldest of the Heartless there and despite being nothing more than hungry instinct in the past, they can still remember, recollect, and gain wisdom from the past. Along with their general intellect being greater than most humans and overall being very powerful, it was only obvious and obvious to every Heartless whether Pureblood or Emblem, when a Darkside speaks, they listen.
Despite this leadership, Darksides are rather calm and are prone to going with the flow, shrinking to speak with others at any-possible time and give advice to more lonely Heartless in the areas around herself. Darksides are usually found where the energies of Demonic-infused Darkness energies are found blowing through the hardest, absorbing and contemplating the various energies around them. However, other thoughts are bound to come up of lust, of love, for another one. Very few men enter the Shard of Darkness not a husband to another mamono, and the few that do enter without one, usually are swarmed quickly before a Darkside can do anything. Their easy-going nature means that very few of them to command anyone to bring a man for them, they're more likely to go do it themselves.
Darksides, if they desire a mate, have an interesting way to go about it, they can investigate sleeping minds alongside the Hearts of living things and are drawn to males with lewd dreams, things that also draw the Shard of Darkness to bring them into the Spirit Realm. They can implant themselves within the dream and make it more lucid, like a Nightmare would, upon which they actually stay like their massive form and one of the first things they do is test the man's combat skills, or the ability to use the fact that they are now lucid dreaming to their advantage. The outcome, however, doesn't change if the Darkside wins or loses, though most times, they win.
In-combat, they have several abilities, their most common of which is to generate Darkness within their fist and slam it down onto the ground. This Darkenss than generates a portal to the Shard of Darkness temparily which calls weak Heartless like Pureblood Shadows and Emblem Soldiers through to aid her in-combat. These Heartless instantly know what the Darkside is after at this point, and don't attempt to rape him or taint his Heart, only to bring him down for her. Another powerful move they can is to generate ball of reddish-orange energy which causes many spiraling missiles of energy to spit out and home at their targets, these missiles tainted with demonic energy blows foes away and drenches them in heat and lust.
Their most powerful move has them kneel down on the ground, arms outstretched to the side, Darkness and Demonic Energy form within the center of her heart-shaped hole as a massive ball and than with a shudder and push, the ball escapes and homes in on their target. A Darkside can usually do this three times before needing to regain their energy, these orbs when impacting with the man or anyone, dazes them into a state of lust and gentle-feeling intoxication, a solidification of their love for the person in-front of them or their husband if used on another foe. If hit by all three orbs, its basically over for the man as he falls over and is unable to get up as he feels far too dizzy and entranced at the massive, gentle-smiling woman at them.
The other Heartless at this point, whether she wins or loses, disappear back to the Shard of Darkness unless the Darkside intends for some group fun with her new husband. The Darkside at this point will shrink down to a much more managable size and approach the man she has chosen. Her cooing words intend to make sure he is not afraid even as he probably struggles if he won as the dream he once thought under his control bends to her whims and shadows come to life to bring him to his knees, clothes disappearing. From there she will take him repeatedly, in multiple positions, changing locales from her and his memories to gain a most enjoyable experience.
A note, the inside of her heart-shaped hole are extremely sensitive and while Darksides won't say it, their most embarrassing part. While they can let the hole stay-there if they wish, once married, Darksides gain the ability to fill this hole in with their magic, making it look like there was never a hole in the first place. Though massaging the inners of it, however weird, will make the Darkside shudder in bliss at its insane pleasure. They also gain the ability to hide within their man's shadow like Pureblood Shadows and Pureblood Neoshadows. Though they can't turn 2D like them, they can still spring from their shadow either in their normal massive form, or their smaller form.
Their hair can also grab at things due to being tentacle-like and can also be used sexually if desired, they, like most unusual bodyparts for mamono, are capable of both taste and smell, so that they may taste his Spirit Energy if they grab onto his body and cock during foreplay. Not as sensitve as their heart-hole, but they definitely enjoy being touched anywhere by their husband of course.
Darksides that encounter non-married men in the Shard of Darkness do not initiate him in combat, though if he meets her fancy she will shrink down and try to converse with him, more specfically about his life and how the outside world is. Heartless mamonos know when a Darkside is near and when one is marked even when she hasn't touched him, and as so, will not even go near the two, even the more instinctive-driven Pureblood Shadow and crazed Pureblood Darkballs want not part of a Darkside's affair. The Darkside herself hopes that she may gain his heart simply by talking to him and entertaining the thought of her love, rejecting or refusing her however, will simply make her visit you in your dreams and the above will repeat itself mostly.
Darksides that aren't married and are in the real world are extremely rare, but not impossible, those encountered will basically act the same, but they become a bit more curious about the world around them and are prone to exploring, forgetting to come back to the Shard of Darkness to direct the other Heartless every once in a while.
Married Darksiders are good, they're really good at the task of being a spouse and a great one at that. Jobs are easy for one of their general skill and memory and their mind isn't always majorly set to fucking and lust and is more than happy to talk about various random-things. They make very good story-tellers even if their stories do get more than a bit dark, might want to work on that, or not.