About - Chiyumi Ten

There is not much known about Chiyumi Ten, but I do know that Chiyumi Ten is indeed her stage name! Her real name is Umi Tenchi shown in this image. In Japanese, it would be said "Tenchi Umi", while her stage name would be said "Ten Chiyumi"... See the similarities?
If the J-Pop wiki is to be trusted, she was born in Tokyo on February 1st, 1957 (making her 27 years old at Kidorikko's formation, and 67 years old now), and her blood type is B.
Chiyumi Ten was the face of Kidorikko; almost literally the poster child, as Kidorikko's albums "C'est L'elegance Na Tanoshimi" and "Ryukou Tsushinbo" both featured photographs of her for their covers.
She had an idiosyncratic singing style, high pitched and very energetic, and when singing for albums she would occasionally include her own laughter, like in Himitsu no Oukurioukami. When performing on stage, Chiyumi would wear colourful, frilly dresses, seemingly putting on an exaggerated persona of a princess, as during the Kodomotachi no City tour she even sported a little tiara! She also seems to have liked cats as well; quite a few Kidorikko songs make reference to cats.
Chiyumi Ten had a truly awesome stage presence. She had so much energy; there was always a smile on her face, and she seemed to constantly move around the stage. I've seen people compare her dancing to Jun Togawa before, and while the two are similarly theatrical, Chiyumi is definitely more cute, and Jun is quite a bit more angry and punk.
Each member of Kidorikko had their own little nickname, and while Ryuichi's and Kimitaka's make a lot of sense, Chiyumi's just... doesn't. It's Kumiko Amatsu (though I've also seen it written as Kumiko Amachi), oftentimes shortened to Kumi-chan. She's actually referred to as Kumi-chan in quite a few places, including on the VHS of the Kodomotachi no City tour.