Kereellis is behind everything
The reason he knows things before they happen? He's planned it all.
Why? That's a matter for another WMG (which I haven't thought of yet).
Sasaki is psychic like Karatsu
She summoned Yaichi and noticed his presence at the end of the ears case, and he saved her twice. Once from the 'suicide song' case from volume 3, and from the ghost in the bride case in volume 8. She even thanks Karatsu for saving her again the second time.
All the main characters are Expies of the main cast of Angel
, minus Angel.
Karatsu: Self-hating psychic with Chronic Hero Syndrome
Sasaki: Sexy, money-grubbing Jerk with a Heart of Gold and unwilling Team Mum - Cordelia
Numata: Tough working-class guy with a secret very soft centre - Gunn
Makino: Cutesy nerd with surprisingly macabre interests and abilities - Fred
Yata: Geeky loser with traumatic past - Wesley