Chichigami Oni was the character by Konoma.
I could've sworn she was a mascot, but according to what few records are left, she was a demon... With heart beat looking horns? Whatever. I hope I'm wrong in thinking she was the original mascot to Yamaha Music and was betrayed and replaced; where Konoma retained the copyrights; and then her creators made an effort to expunge her from history.
She was supposed to be the rival of Miku and Sonico? Pretty sad when Kadokawa Games came up with Kantai Collection which pretty much rivals Vocaloid and Touhou in many ways but especially in character design.