Chained Soldier succeeds because it never pretends to be anything other than what it is. The chains are real, the fights are solid, and the rewards are... very, very thorough. Search the keyword with the understanding that you are entering a world where fan service is the lore.
At the heart of the series is the "Slave" ability, which allows female members of the Anti-Demon Corps to transform the protagonist, Yuuki, into a powerful monster. This transformation comes with a biological catch: the "Master" must provide a "reward" to Yuuki after a battle. Chained Soldier Fan Service