Viktor's Plan

Challenger tower, a fantasy game-like place where people called hunters or players climb to obtain otherworldly items and to gain their level. This type of tower exists in so many multiverses except earth because the earth has nearly lost its ability to hold mana.

As the mortal realm's logic, the tower works the same. But there are some differences between a mortal realm's tower and a heavenly realm tower. 

The tower inside the sky realm only takes one person in and closes its door. The challenge may take more than a few decades and the challenger can only come out once he finishes the 30th floor. Before that, he can not come out. 

The only way out of a tower without completing the quest is suicide.