The Most Powerful Summoning System

The royal prince starts the game, but his father dies. However, as an only child, I did not inherit the throne, but was robbed by someone with a foreign surname, and the throne was taken away from me for three years? The protagonist is still guarding the tomb in the imperial mausoleum. And the predecessor died inexplicably. Let's see how the protagonist gets into trouble with the help of the system. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.