Cellphone Charm is the signature rumored charm in the School Days series.
- "They say if you take a picture of the person you like and set it as your wallpaper,and nobody else finds it for three weeks,then your dream will come true."
- — Sekai explaining to Makoto about the Charm
In order for the charm to work the user must secretly takes a photo of their crush and set it as their wallpaper,then within three weeks their crush in the picture will surely falls in love with them.So far no one who attempt this charm had been fulfilled and the only known persons attempt to do this are Makoto(unintentionally),Sekai,and Hikari.
Makoto secretly takes a photo of Kotonoha during his train ride to school while she was busy reading though he only did this so that it makes him happy just to watch her from afar.Due to Sekai's intervention it's unknown whether or not his so called charm has been fulfilled.
It's revealed that Sekai had a crush on Makoto at the start of the High School and attempts to do the charm on him but on the second semester she realizes that her targeted crush(Makoto) had interested on someone else(Kotonoha) causing her to decide to "Help" him on getting them together.
She reveals to Sekai and her friends that she attempted the charm on her long time crush in junior high but no avail between them.