As of February 1st, the cost to ride the Kumamoto City Street Tram has increased from 150 yen to 170 yen. Child fare has increased from 80 yen to 90 yen. Commuter passes have also increased in price accordingly.
The one day tram pass is still 400 yen, but will increase to 500 yen on April 1st.
You can find more details on the Kumamoto City Transportation Bureau website (Japanese only).