Keiko is the mother of the Shinonome children in the Eiken series. Like most of the girls in the series, two daughters and even her son, she have feeling for Densuke Mifune despite being way older than him, and tried to seduce him.
Keiko used to be a legendary TV idol working under the name 'Hoshino Jun' during 1980's and lived in Zasshonokuma city. However, she quite the limelight as there wasn't a high demand for big breasted women. However, even when Keiko quite she was still popular, but she was't seen in on TV again She married and had several children and Chiharu Shinonome is the eldest of them. She started to work at factory to provide for her children. At unknown point her husband either died or left her as he was never seen or mentioned.
While on her way back home Keiko noticed that she lost her wallet. Keiko tried to search for her wallet and pumped into Densuke Mifune who was on his way home. Mifune accidentally groped her, much to his embarrassment, but Keiko wasn't angry or concerned about herself and asked him if he was alright. Keiko, after seeing that Densuke is fine, returned for the search for her wallet. Densuke offered to help her as he had a lot of time to spear. The search started to follow the places that Keiko went throw: the park were she swigged and built a mountain of sand and going to the river and steeping into the water. While searching in the water Densuke accidentally saw Keiko underwear and due his embarrassment he tried to avoid seeing anymore and fell into the water and groped her again. Embarrassed more than ever, he left the water at once while apologizing. However, this lead to him finding the wallet next to the river. Both of their cloths were wet and had to be dried, and while Densuke used the towel Keiko took off her cloths of and let them dry under the sun which made Densuke give her the towel back and the way she put it on he remembered the photo he saw earlier and after seeing the photo again he find out that she is the idol 'Hoshino Jun'. Seeing her picture she got on Densuke from the back and put her breast on his back, much to his embarrassment, to see her photo and find it to be nostalgic to see how she looked like in the past. "Hoshino Jun" was happy that aboy in the age of Densuke now her and had her picture as she has long retired. At that moment her daughters Chiharu and Yuriko pass by and saw that Densuke is with their nearly naked mother. Yuriko made clear that she suspect that there was something bad going on, but her mother explained what happened to her. After knowing that Densuke is the same person who's Yuriko always talk about she asked if he is the same who Chiharu talks about which caused an embarrassed Chiharu to accidentally to push him into the water.
Densuke was contacted by the youngs of Shinonome who asked them accompany them to the pool. Densuke believed Chiharu would be there but was surprised that Keiko is the one who will be going with them. While waiting for the children to finish, Keiko suggested that they should go into the pool too. Densuke was very embarrassed to be seen with an older woman in the pool of the grown up. After that Densuke waited with children while a happy Keiko went to by some drinks and was surprised to see someone from her past, The CEO.