Mc is a highschool boy with short hair and glassess.

He is an heir to famous wealthy group that kinda monopoly japan economy. He attends elite school where all rich kids enroll. Mc have little sister who was in elementary or middle school.

One day he followed a blondie male students and ended up in weird place. He got into a trap and mc die. Mc then revives by supernatural being like clown or something that explain mc was in another dimension at his school. He needs to always enter the dimension again, fight other students who share same fate with him to gain points so he can survive.

Mc heart begin hurt so much and he will die if he did not enter the dimension for certain period of time. Mc power is gambling. Mc will make a room and only him can enter, he then make bet with the dealer of that room, mc can bet anything from his money, watch, house, etc but rather mc found out the more risk he bet, the bigger chance he win so mc always bet his life. The dealer will roll dice, and mc will predict odd or even after betting something, if mc win the bet, he win the fight, losing the bet will make mc lose the thing he bet on. Time were stopped when mc enter the room so it is OP power.

Mc later has party member on that dimension to help him....his female classmate who has crush on him, who protected mc from blackmail where it say that mc was adopted, her power is playing koto instrument and attack the enemy using her music.

The blondie male students who was handsome but got bullied hard in school because of his timid personality, he have tragic past of being abused by his mother. His power is drawing to manifest it and attacking them with it.

This 2014 or 2015 manga, already finished with 4 or 5 volumes and seems axed. Mc little sister also involves with the game. I remember the name have game oukoku on it... thanks for reading and hope som1 can find it.

found it, it is fictional king