Write SQL query to solve given problem: Show the id of game platform which makes the most sales in Japan.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T.game_platform_id FROM ( SELECT T2.game_platform_id, MAX(T2.num_sales) FROM region AS T1 INNER JOIN region_sales AS T2 ON T1.id = T2.region_id WHERE T1.region_name = 'Japan' ) t