Todomomo

Rei: not being accepted into UA
August: death
Hino: a germaphobe
Haruhi: Rei
Eve: literally a tiny goddess, she fears nothing

Kirimina

Akane is scared of Chuckee Cheese
Iro is afraid of letting people die

Miruhawks

Dove is afraid of ending up like her parents, that's why she ended up in the support course

Iidamei

Tameiko is afraid of really nothing

Kamijirou

Stormi: being rejected
Riitsu: water

Dabi x Toga

Roman is afraid of being mistreated for being Dabi's son. I mean, he faces his fears everyday but it makes him feel worthless

Nejitama

Amai is afraid of being seen as weak and worthless.
Phoenix is afraid of being forgotten

Mt.Kamui

An arachnophobe

Ryushot

Megami is afraid of ghosts.
Daenerys is afraid of being forgotten.

HitoRei

Rosalind is afraid of being abandoned because her parents are so different from her.

AkanoKaguya522 made this Headcanon.

Tetsukendou

Elliot has tribophobia. That thingy where your afraid of holes.