Risa Kanzaki is the wife of Takeshi Nagase and the mother of Arashi Nagase. In Episode 6, when Arashi arrives home 15 minutes, a woman greets him, whom he treats as family. This is later clarified by Hiroyuki Tokumori's comments in later episodes to be Arashi's mom. She also knows Hiroaki Tokumori (Yuki's father) from the previous series.
Risa is also a character from the original series Gokinjo Monogatari.