(Translated by https://www.hiragana.jp/)
The Wayback Machine - https://web.archive.org/web/20160225013819/http://www.toyota-global.com:80/innovation/safety_technology/safety_technology/technology_file/passive/srs_airbag/seat_cushion.html

SRS Seat Cushion Airbag

The front end of the seat cushion will lift when the airbag inside deploys during the frontal collision. This will improve the passenger's restraint efficiency by working together with the movement of a seatbelt to restrain the waist from moving forward.