What kind of uncle would the UT/UF/US/SF skelebros be to their brother's kid?
UT!Sans: He’s the chill uncle. The one who brings cringe-worthy gifts (shitty gag stuff he picked up in gas stations) and embarrasses you with those awful nicknames from when you were six, but who’s there for you. Great help on science projects, even if he’s constantly enforcing nap breaks in the middle of it. When Papyrus’ kid(s) is (are) younger, they always want him to babysit because he lets them watch TV all night and eat like garbage. He never pushes you to say what you’re thinking, but he’s pretty good t picking out when you’re in a low place. He doesn’t try to be your therapist, but he’ll check up on you, make sure you’re eating right. He doesn’t tell Papyrus if you don’t want him to and if he doesn’t think you’re in a dangerous enough place that he needs to be told. Your dad can be a little much when you’re shutting down. But he’s pretty used to keeping secrets from his brother. At least this is one he won’t feel as guilty about.
UT!Papyrus: The hype uncle. He is always really enthusiastic about whatever you’re doing, to an embarrassing extent. He shows up at your childhood soccer games wearing the team colors. Tests? His house is always open as a place of study! He’s constantly trying to get you interested in either puzzles or pasta, but honestly he’s about anything you’re into. Being babysat by him essentially means also being babysat by Undyne, and things tend to get wild. He will always make certain you are Hydrated. Always trying to make sure you avoid picking up your dad’s lazy habits. The Ultimate Pep Talk giver. He believes in you 110%, and he want you to too.
UF!Sans: He doesn’t totally know what to do with you before you get old enough that Papyrus stops shooting daggers at him for swearing in your presence. Red doesn’t deal well with little kids. You mostly remember him as a rough laugh after a joke that you don’t totally get but has your dad red-faced and yelling, a voice yelling at you to get off the fence if you don’t want a broken neck, a strong hand pulling you out of danger or ruffling your hair on his way out the door. You get closer once he starts feeling like he can talk to you more or less adult to adult. He’s a good person to go to when you just need to get away for a bit. He loves your dad as much as you do, but he gets that he can….be a bit much. If you ever get in trouble, he’ll give you a ten minute dressing down and likely cuss your ass out, but he won’t tell your parents unless you’re in real danger. Any s/o’s that hurt you have him to reckon with. He won’t ever tell you that he loves you, but he’ll show it constantly, and a “heh, proud of ya, kid” goes a loooong way with the two of you.
UF!Papyrus: The involved Uncle. He is constantly in your business. He likely knows your class schedule better than you do.He doesn’t totally trust Sans to be as updated as he should be about your activities, so he picks up the slack. Is constantly going to battle for you. Bullies? Unfair teachers? Bitchy exes? Things of the past. Let them try messing with 6 feet 7 inches (11 inches with his heels on) of skeletal bad temper. But don’t think you’re bullet proof from his scoldings. You are a constant recipient. Still, being his nibling gives you a little more leeway than a brother or a child. Sniffle a bit, and he’ll likely stop and mutter something about how you probably get the point now. He want you to live up to your potential, even if he can choose a dickish way of expressing it. His gifts are rare and holiday limited, but thoughtful.
US!Sans: When you were a kid he was your idol. He seemed like a superhero. Strong. Brave. Kind. Short enough that he seemed to understand you better than the other adults (although you learned not to mention this observation to him). He had your boundless enthusiasm, and more often than not he was more playmate than adult figure. Then you grew older. And you fell into the trap so many people did. You mistook his openness for naivety, his optimism for childishness. You began to feel like you had to protect him, not he you. It kept going, until you got hurt. You were scared, you didn’t know where to go. And its then that your hero returned, there as a shoulder to cry on.
Also he teaches you to cook and color-coordinate like a boss.
US!Papyrus: The Bad Influence ™. You learned from him how to talk your way out of basically anything and run from what you couldn’t. He gives you sweets whether or not you’re supposed to be eating them. He lets you stay up way past your bed time. Anytime he’s left in charge is a time when you can keep your room however the flip you want. And you can get literally anything out of him if you catch him smoking around the house and promise not to tell your dad. Spoils you senseless. He’s not the most responsible of guardians, but he helps you have fun and reminds you not to take life too seriously. He’s good at helping you talk out your insecurities.
SF!Sans: He teaches you how to fight. If you’re not that physical a person he may be a bit of a nightmare for you but any training you express an interest in, he is there for. He’s oddly kind of affirming? I mean, its mostly also a back-handed compliment to himself but still. “BUT OF COURSE YOU’RE ACCOMPLISHED. YOU’RE MY NIBLING!” Any potential s/o’s have to go through his screening first, a daunting task that has chased off many an asshole. He abjectly refuses to let you take any of life’s shit lying down.
SF!Papyrus: Quiet, but non-judgemental. You’re not sure what it is about him, but he can get you to spill your guts about anything while still somehow respecting your privacy. He helps you roll your first joint (waiting until you’re old enough). He’s always honest with you, even on the questions that make most other adults turn away and blush, or tell you you’re not old enough. Through processes none of them fully understand, all of your friends have his number on their phone, but its come in handy more than once when you need to be picked up and you’re in no fit state to pick up the phone. He keeps every present you’ve ever given him, including those awful painted mugs from when you were four years old.