Lucifer
Being brought to heel isn't in his nature, so Lucifer feels particularly wrung-out after you've had to control him and his brothers with the pact, he'll feel quite miserable beyond what he believes is a reasonable reaction for being physically achy and sore. He doesn't trust himself to hold a conversation without somehow revealing that he's upset, so he'll retire to his room without anyone noticing he's left. If you follow him, he'll muster a "what do you want?", though there's hardly any bite to it.
If you tell him what you want is to make sure he knows you love him, Lucifer poorly contains his surprise. This is all he really needs- to know that he's cared for and special to you, and that you need him a little bit too. Though he doesn't say too much, he'll appreciate it if you say this a few more times throughout the night, just quietly reminding him that he's cherished by you. He can't hold back a small, satisfied smile if you mention he's your number one, and he might ask "hm, is that so?", hoping to hear it again. You can see when he starts to feel a lot better when you gently place your arms around his neck and hug him cheek to cheek, he'll give a warm but genuine smirk, saying "careful, or I won't let go..." and then "alright, I believe you... thank you for humouring me".
Mammon
He's the most familiar with the effects of the pact, Mammon would actually feel more disgruntled if you ever brought the others under your control and he wasn't there and missed out. Though he admits he feels a bit achy afterwards, he associates this with your bond and it reminds him that he's happily yours. That doesn't mean he doesn't appreciate you checking on him though, he'll blush deeply and quietly murmur your name when you ask if he's okay and say that you're going to stay with him for a while.
If you ask where he feels sore and then kiss those spots, Mammon will softly laugh and gruffly say that you're spoiling him. When it occurs to him that humans can actually feel just as many ill effects from using the pact as demons, he'll suddenly become quite gentle and protective, getting you a sweet drink and saying sugar is good after this sort of intense experience. Mammon will be quietly attentive with you all night when he realises you're probably a lot less familiar with these sensations than him, you tell him that you love him and you learn a lot from him about aftercare that evening too.
Leviathan
Levi is a mix of anxious and hyper after he's been controlled by the pact, he'll be jumpy for no reason and he feels like his concentration is all over the place if he tries to focus on anything. He also feels hypersensitive to touch, even accidentally brushing against his arm will make his skin prickle.
Since he's finding it hard to make decisions about what will help him, you just quietly and gently tell Levi what you're going to do, and he can nod or shake his head to tell you yes or no. You tell him you're both going to go for a walk outside, with no music or lights or other overstimulation. After you walk slowly around a familiar area, you can lay together on the grass, which feels more grounding than inside the house. You look up at the stars for ages, and Levi eventually reaches for your hand as he starts to wind down, needing this little bit of connection between you. He'll turn his head to you and smile, saying that as a demon he isn't used to feeling like this, but he never wants this bond between you to end.
Satan
He starts shivering quite a lot after being under the pact, Satan isn't used to feeling like this so he doesn't really understand what he's experiencing and doesn't do anything to fix it. When you visit his room and see him visibly trembling, you quickly wrap the two of you in a blanket, telling him you're so sorry you didn't realise sooner. Satan looks perplexed, not feeling that you owe him an apology but appreciating that you clearly care about him a lot. Satan tucks his face into your neck while you hold him and try to warm him, shakily telling you how much you mean to him and how the emotions you make him feel often make him realise he's more vulnerable than he thought.
He appreciates if you gently rest your hand at the back of his neck, as if you're holding his head against your shoulder or running your fingers through his hair. You drift to sleep together for a moment, and when you wake you see Satan's now in his demon form, looking blearily surprised at himself too. His tail has wound quite sharply into your leg, which can sometimes be painful when Satan doesn't watch himself. But he takes a deep breath to relax and loosen his grip, apologising for babbling anything silly earlier but saying he wouldn't take it back, he knows he was shaken up but he sincerely meant it.
Asmodeus
You controlling him with the pact was very exciting to Asmo, he's keen to tell you all about how it felt for him and ask if you maybe felt the same. When you ask if he's hurt or sore at all or if he wants a massage to help him relax, Asmo just sheepishly chuckles and says you're going to have to stop offering such things, you using the pact was already more than enough.
Even though he phrased it in a teasing and joking way, Asmo feels relieved after being honest with you about his feelings. When you just laugh and tell him he's being cute like this, Asmo feels even more grateful and happy, giving you a cuddle and saying whatever you want to do tonight, even if it's just playing board games, he's all yours.
Beelzebub
When you go to check on him, the first thing Beel does is assure you that he's not mad at you for using the pact. A huge weight lifts off his chest when you say that you never thought he was mad, and that you're here to look after him.
You realise he's feeling emotional and you ask if you can sit with him for a while, you also mention you brought some food in case he needs it. But Beel's face falls, he mumbles that he'd want to see you just as much whether you brought food or not. Then Beel apologises for saying that and getting upset, saying he's been like this all night and it's not your fault. Before you can reassure him, he blurts out that he's sorry for all the times you've had to see him having a tantrum about food, saying he wishes he could help that but he can't.
Even though you want to tell Beel that he doesn't have to apologise, you also wonder if this is something he might've felt bad about for a while. And so instead of shushing him, you sit with him and ask how it feels when he loses control, and whether anything like this ever happened when he was an angel. Beel sadly shakes his head, saying there were maybe a couple of things here and there, but nothing like now. You can tell he's really glad and relieved to talk to you about this, and he says that if he's ever acting in such a way that could actually hurt someone, he hopes you wouldn't hesitate to use the pact. You know in your heart you'll never have to fear this from Beel, but you nod, telling him you'll keep his promise until he can trust himself as much as you do.
Belphegor
Belphie doesn't mind you using the pact on him, though he wouldn't like any of those sensations if they were inflicted on him by anyone except you. He gave himself to you and he meant it, no matter what. If you ask how he's feeling he'll be completely honest, giving a soft laugh and saying grumpy and sore. But then he'll ask how you're feeling, he genuinely sees that as far more relevant and definitely more important to him.
If you also say your body aches, he'll give a small grin, then suggest that since you're both feeling like garbage, why don't you torture yourselves further by eating sour lollies and extra-cold ice cream while watching a terrible devildom tv soap. This is exactly how you spend your evening (you also take it in turns to close your eyes and feed each other either ice cream or combinations of weird candy, so you never know what you're going to get). This often ends in Belphie cracking-up and having to cover his mouth so he doesn't spit your strange and horrible combinations out, and by the end of the night your cheeks hurt from smiling, you both feel a hundred times better and are newly obsessed with whatever terribad tv series you found on Belphie's phone in the first place.