heisei retro
平成レトロ 女児服 平成女児 heiseiretro cutecore
Aesthetic and fashion style based around nostalgia for the Heisei period, primarily featuring elements associated with '90s and 2000s Japanese childhood, especially that of young girls and the clothing that was marketed to them during the time. It is closely related to Yume Kawaii and Y2K fashion. In the West, it is often referred to as "cutecore".
Common themes include chibi animals and mythical creatures such as unicorns, rainbows, bokeh and sparkles, stickers, charms, colorful plastic jewelry, randoseru, sweet food such as fruit and cake, bright pastel colors, shaped hairclips and hair bobbles, magical girl themes, and symbols such as hearts, stars and musical notes.
Brands like Mezzo Piano and Angel Blue are popular, as are Sanrio characters and Tamagotchi, and flip phones, especially with cellphone charms.
For specifically adults wearing children's clothing, see jojifuku. (Do keep in mind, however, that the 女児服 tag is often used for both concepts on sites like Pixiv.)