Futoago (双子) is a japanese aesthetic that consists of all forms of "twinning".
The practice of futago first started in 1958 due to the debut of the japanese singer duo The Peanuts. They were identical twins not only in their appearance but also in their outfits. Their name was choosen in order to reflect that twinning, a peanut containing two nuts in a single shell. The only way to distinguish between Emi Ito and Yumi Ito was that Emi had a mole that Yumi had not.
However, it wasn't until the mid-1990s that futago spread in popularity and became a trend. Around the same time, twin outfits began to be featured in fashion magazines, and NHK airing of the american soap "Full House" further increased the boom with the Olsen sisters (Mary-Kate & Ashley). This lead to a sudden twin boom on TV, such as ManaKana (Mana Mikura and Kana Mikura) and Osugi and Pico.
Wearing the same outfits has been popular for several years mainly with the younger generation. However, in futago, you not only wear "similar" outfits but ones that look almost identical to your partner's with little differences, such as color or print. Different to the couple outfits that are often done by lovers or married couples, twinning is usually done between close friends.