Maou no Hajimekata is a Japanese novel that begins with a sorceror, whom after decades of research discovers how to manipulate a source of infinite magical energy, which then allows him to do a number of things including the extension of his own life; summoning and binding of demons to do his bidding; construction of a gigantic labyrinth and dungeon as a base of operations; and cast massive offensive spells.
The story gets a bit dark after the first arc, but the main character gets in to all kinds of mischief as he encounters monsters, demons, adventurers, and all manner of races you typically find in a fantasy setting.
The MC builds a sort of harem along the way. Some methods are more amusing than others. The novel is definitely more descriptive than the graphic novel. The MC uses his harem as a living, mobile battery to store magical energy. He drains the magical energy to refill his magical power when required.
Chapter 15: I can't believe the fate of Yunis. Bloody hell this author is savage as heck! Also Aur adds more to his harem.
Note to self: Read up to
Chapter 15.5: Dungeon Commentary.
Might have to revisit this in a few months as there are no more translated chapters at this time!