According to the official website, the cast for Nishizono Mio
in Little Busters!
was announced to be changed from Kawaragi Shiho
to Tatsumi Yuiko
considering the health of Kawaragi, who recently became pregnant. Kawaragi said she's six months pregnant and the condition of the baby is stable.
Sources: Little Busters official website
, Kawaragi's official blog