Oricon reports that Yuko Mizutani passed away on May 17th following a previous diagnosis with breast cancer. One of Mizutani's most famous roles was Sakiko Sakura (older sister in TV anime, Chibi Maruko Chan), as well as Sora Takenouchi in Digimon Adventure.
Her most recent stint was voicing Ikuko Tsukino in Pretty Guardian Sailor Moon Crystal. Mizutani's also performed some video game voice work as Iris in Mega Man X4, and the Japanese voice of Minnie Mouse for the Kingdom Hearts series.
Mizutani was an extraordinary talent, she'll be missed dearly, and may she rest in peace.