My Beautiful Teacher - Chapter 366

As the heir apparent of the Ye family, Ye Xuan went through fire and water for his family, but Ye Lang, who had just awakened his Divine Soul, usurped his place. In order to keep his position, Ye Xuan challenged Ye Lang to a Life-death Duel. With the broken Dantian, would he win this fight? The black ring his mother left brought him a great opportunity: Realm Hell Tower, where he met a mysterious lady, who told him to look for nine Daoist Laws to enhance his strength and gave him the Spirit Heaven Sword. Could Ye Xuan find all the Daoist Laws and become a powerful swordsman?

- Description from Novelupdates

In regards to the MMORPG Cross Reverie, Sakamoto Takuma boasted an overwhelming strength that was enough for him to be called the Demon King by the other players. One day, he gets summoned to another world with his appearance in the game. There, there are two people that insist “I am the real summon master.” Takuma gets slave-turning magic used for summoned beasts cast on him by the girls –

There are always four kinds of people in the traditional Mary Sue world. The Male Lead, the Mary Sue female lead, the woman who never wanted to see the female protagonist live a good life, and the infatuated man willing to destroy heaven and earth to get the female lead.