this is are suggestions to glance at before writing up a history. these are only bare minimals that could be used as an excuse to have interaction between the characters of different mangas. if you have your own ideas, go ahead & shoot.
note that these situations are neutral feel free to have the characters hate or love one another.
Yukari (aka, Caroline) Hayasaka; knows Nana Komatsu due to a family-friend situation between their families.
George Koizumi; familiar with Tetsu through their fathers.
Daisuke (aka, Isabella) Yamamoto; is familiar with Hotaru.
Ken Nakagawa; is familiar with Mikako due to the resemblence between Tsutomu and him. Or, familiar with Trapnest due to a sort of celebrity familiarity.
Hiroko Maki; knows people at the Yazawa School.
Masashi Sakamoto; knows people at the Yazawa School.
Yuko Mamiya; see Mariko.
Nana Komatsu; see Yukari.
Nana Osaki; see Risa.
Ren Honjo; see Ken. see Risa. see Miura.
Takumi Ichinose; see Risa. see Miura.
Nobu Terashima; see Risa.
Reira Serizawa; see Risa. see Miura.
Mizuki Mochizuki; works at Happy Berry.
Hotaru Shiraishi; see Isabella.
Tetsu Sugisaki; see George.
Masaki Miura; familiar with Trapnest through his celebrity connections.
Mariko (aka, Body-ko) Nakasu; family friend of the Mamiya family.
Risa Kanzaki; familiar with BLAST & Trapnest.
Mai (aka, P-Chan) Oota;
Jiro Nishino; familar with Yasu.
Hiroaki Tokumori; Familiar with Junko.