Fan Nickname: Before Seto's official name was revealed, most fans took to calling him "Forest-kun" in reference to Imagination Forest, the song he debuted in.
Haruka was called "Dead-kun" by the English fandom before his official name was released based on the Children Record PV where there's one scene he appears in where he lying on the ground looking dead.
Takane was nicknamed "Actor" based on the pv "Headphone actor" until her official name was released.
Kuroha is a Fan Nickname since he still currently lacks a canonical one. Some merchandise call him Black Konoha, Dark Konoha, or Konoha? though.
Mekakushi Trio or Orphan Trio forKido, Seto, and Kano, and Yuukei Quartet for the high school kids Shintaro, Ayano, Takane, and Haruka.