What is the genre of the game titled '999: Nine Hours, Nine Persons, Nine Doors' ?
genre of the game refers to genre_name; '999: Nine Hours, Nine Persons, Nine Doors' refers to game_name = '999: Nine Hours, Nine Persons, Nine Doors';
SELECT T2.genre_name FROM game AS T1 INNER JOIN genre AS T2 ON T1.genre_id = T2.id WHERE T1.game_name = '999: Nine Hours, Nine Persons, Nine Doors'