Item Cheat na Dorei Harem Kenkokuki

Item Cheat na Dorei Harem Kenkokuki (アイテムチートな奴隷ハーレム建国記, lit. "Independence of a Slave Harem With Item-cheating") is a light novel series by Nuko Nekomata with illustrations by Natsuna Natsu.

Plot
High school student Rindou Shouma was summoned to the other world, Astral, where duels called "Oracle Game" decide everything. However, the rules of the card game were exactly the same as a card game Shouma was already good at! At that point, undefeated Shouma decided to create his own paradise full of liberated slaves.

Creating a harem kingdom with the power of cards, this is the independence of a slave harem with item-cheating!