Uh I had a bad feeling seeing the cover and the first chapter confirmed it. It's kinda yikes to start off like this without any synopsis lol.
Anyways here's supposedly a synopsis of it from Novelupdates
Yamada Ichiro, who was summoned to another world, and the black-hearted handsome Ryuguin.
The appraisal results show that Ryuguin is the hero and I am the Holy Knight.
While the hero Ryuguin is playing around without making any effort, I’m always full of scars and tattered because I went out to clear the labyrinth countless times to save the world.
Even though I helped the growth and passed through the line of death together with the heroines, they all stuck with Ryuguin for some reason, confessing to Ryuguin in front of me and jumping into his chest.
The number of Ryuguin harems is increasing.
This story is about me jumping out of Ryuguin’s harem party and doing what I want to do
(At least silver lining is it's not gonna continue like this, still wouldn't read it though)