Manga Debut: Chapter 31

Keiko Yozakura is the Grandmother of the Yozakura Family and the previous 8th head.

Keiko was the 8th head of the Yozakura Family when she met Ban whilst he was living recklessly, and they later on started dating. They eventually got married and had Rei as their child.

(Source: Mission: Yozakura Family Wiki)