Data Sim Card at Kansai Airport. A 30 days 3GB sim card can range from 4000 yen to 9000 yen. I pickup at TRE (3GB 30 days) at JAL counter for 4500 yen. Saw another similar package selling for 4000 yen at the vending machine.
PS: Cheaper options are available in town, selling at places like BIC Camera.