>>16345597the giant undershirt + fitted/semi-fitted vest + wide pants/skirt was really in over the last year or so. you can see some other examples of it (and other "baggy chic" type styles) here
https://smartlog.jp/52982it was more popular with women than men, but guys who like more cutesy styles tend to go for it.
fuwa's roommate seems to generally go for bigger, baggier clothes--i wonder if it's because he supposedly used to be fat and is maybe still a bit insecure with his body, but huge ゆったり fit has been all the rage for like 3+ years now in tokyo so who knows maybe he just likes the look. 