Jirai Kei is a fashion style also known as "Landmine Girl". Style-wise, you'll see black combined with pink or white, frills, and chunky shoes, and Sanrio plushies, especially Ruromi. They're also emotionally dangerous, and are associated with smoking, binge-drinking and self-harm, which is where the "landmine" tag comes from. Memory and Mikeneko would be good examples of Jirai Kei-themed vtubers, IMO.Rie got "My hobby is dressing up as a landmine at night" What did her friend mean by this?
If you want a deeper explanation, here's a fun stream by Lia about the subject:
With that explained, Rie would totally be a Jirai Kei girl after hours.