Sekiko Ushirono (後野 席子, Ushirono Sekiko) is the fandom name given to a background character who appeared in Tokimeki Memorial. Her name literally translates to "Girl from the seat behind". She is the girl sitting behind the protagonist in the opening scene of the game.
She earned some popularity among the Japanese fans, who initially thought she was a secret character. A short story featuring her was published in one of Konami's magazines.
In Tabidachi no Uta, a girl resembling Sekiko appears sitting behind the protagonist in the opening scene. However, her hair has a blondish tone, and it's hard to tell whether she has freckles.