Database: video_games
Question: What is the title of the game that gained the most sales in Japan?
SQL: SELECT T.game_name FROM ( SELECT T5.game_name FROM region AS T1 INNER JOIN region_sales AS T2 ON T1.id = T2.region_id INNER JOIN game_platform AS T3 ON T2.game_platform_id = T3.id INNER JOIN game_publisher AS T4 ON T3.game_publisher_id = T4.id INNER JOIN game AS T5 ON T4.game_id = T5.id WHERE T1.region_name = 'Japan' ORDER BY T2.num_sales DESC LIMIT 1 ) t