My Isekai Adventure

Kai Kasugi, a young scientist is assigned a job to research a portal which suddenly appeared in Tokyo, which connects two worlds. The portal takes a person to a random destination. The scientist team which was assigned the work decides to send someone to the other side. But after a series of events Kai is betrayed my his fellow scientists out of jealousy and he is forcefully thrown into the portal. Kai falls into despair realizing that his life has now ended but little does he know that to his luck or some supernatural power he ends up inside the most secure place existing on the other side- the treasure room of the long dead demon king Yasur. Genre: Fantasy, Mystery, Harem, Romance, Action