it's law (jenlisa oneshot)

Jennie thought nobody had ever understood her better than Jongin did, not only mentally but physically. That was, of course, until she met Lalisa Manoban. Her boyfriend had only partially introduced her as his "stuck-up, boring but somehow also annoying half-sister" who he had "only talked to twice in his lifetime". In response, Jennie asked him to invite her to a family dinner, so she could meet her and maybe they could make fun of her together, as they did with everyone else they disliked.
Of course, Jennie being Jennie, the second she laid eyes on the 23 year old, dark haired girl, she decided she would actually make an effort. That effort turned out to be continuous hook-up sessions.