SO I HAD A THOUGHT AND IM GIVING IT TO YOU BECAUSE YOURE THE BEST!!! So any soulmate au where once the youngest one turns 18 you find out who the other is OK SO the day before his, Enjolras decides he doesn't want his life dictated by pre-determined rules, so he impulsively marries his boyfriend, Grantaire. As soon as they wake up the next morning, they see that [enter whatever soulmate au: tattoos, quotes, whatever] matches.
[Shhh, you’ll make me blush. I’ve never written a soulmark au! Here it goes:]
“Are you really sure about this?” Jehan asks doubtfully.
“Yes,” Enjolras says firmly.
“Believe me, Jehan,” Combeferre says with a slight grimace. “This is already the toned down version of this plan.”
“He wanted to get married, today,” Grantaire says, grinning lovingly at his obstinate boyfriend.
“Isn’t there a two week waiting period after you register a marriage?” Jehan frowns.
“Yes, yes there is,” Combeferre says. “And with good reason.” That earns him a scoff from Enjolras.
“So tattoos it is,” Grantaire grins widely.
“Alright,” Jehan laughs. “I do think it’s super sweet.”
Enjolras gives them an enquiring look. “You don’t approve though,” he says. He doesn’t sound accusing or resentful, he’s just asking.
Jehan hums vaguely, putting the appropriate paperwork down in front of their friends. “I have good reason to be fond of soulmarks,” they say and their hand absentmindedly passes across their heart. Just above the low collar of their shirt the top of the letter M is visible. “But you guys were obviously meant to be together.” They smile. “And chosen soulmarks… That’s just too romantic for me to object to. I love it.”
Enjolras looks content and Grantaire grins. They sign the paperwork and hand it back to Jehan.
“Right!” Jehan beams. “Let’s get you ready for some ink then.”