Short answers, pulled from the story.
Noir Stardia is the main character of The Hidden Dungeon Only I Can Enter. He is the third son of a minor noble family who possesses the Great Sage Skill that grants unlimited knowledge but causes him constant physical pain.
Emma Brightness helps Noir Stardia by kissing him to alleviate the pain caused by the Great Sage Skill. This physical affection generates Life Points which are essential for his survival and allow him to use his powers without dying.
Olivia Servant gave Noir Stardia three new skills called Create, Bestow, and Edit. These abilities allow him to upgrade his own power and the power of others but require him to expend Life Points to use them.
The first volume of The Hidden Dungeon Only I Can Enter was published on the 1st of August 2017. The series was originally a web novel on Shōsetsuka ni Narō in January 2017 before being acquired by Kodansha.
The anime adaptation of The Hidden Dungeon Only I Can Enter was produced by Okuruto Noboru. It aired from January 9 to the 27th of March 2021 on the Animeism block and was streamed worldwide by Crunchyroll.