"Sensei" debuted in July 1972 and peaked at No. 3 on the Oricon weeklies and was the 30th-ranked song for that year. It was lyricized by Yu Aku（阿久悠）and composed by Minoru Endo（遠藤実）. She would appear on the Kohaku singing that song, but it would be 18 months later at the end of 1973....possibly because of her very young age. Even now, any underage kids performing at the Kohaku Utagassen do so at the beginning of the show since the law states that they cannot do so past 9 or 10 p.m. I'm just not sure where the dividing line is, though.
Had something similar to the story in "Sensei" happen to me back when I was teaching junior high school in Japan. Some unknown admirer left some Valentine's Day chocolates for me...in my shoebox in my shoes. Not the wisest of moves....an added funkier dimension was infused into those eggs some hours later.