This tag represents the Levi (AKA Rivaille) and Eren relationship, characters from Attack on Titan. Please note this article may include spoilers.
This relationship often includes a lot of DV, suggesting that fans like to portray them in a slightly abusive relationship thanks to a training scene in the 5th volume of the Attack on Titan manga.
After Eren discovered his titan shifting ability, humankind were scared of him and he was put on trial on whether he should live or die. Levi tried to convince the court that he could control him and that Eren was an ally of humankind. To further his point, Levi went as far as beating up Eren to show that Levi was in control, leading to many pixiv artwork of these two characters in an abusive relationship. Levi is often shown as a sadist in the relationship.
Afterward, Eren was put under Levi’s watch, saying that he would close watch Levi, and many fans took that as innuendo or proof of Levi’s affection toward Eren. Levi commanded that his team will protect Eren at all costs as Eren was their “trump card.”