Well, I think it was a game, it's been some time since I read it. Let me explain.

It revolves around a male protag/mc who was once bullied/is still bullied by a certain girl. However, one day, out for no where he gets a mysterious letter saying they have a chance to take revenge on someone. Thus, after accepting, he and his "target" are "kidnapped", taken to a certain hotel like building, where the mc wears a mask and enters a torture room type place connected to the mc's room, where he sees his "target" chained to the floor.

As time goes on, things are explained, how he is not the only person in this place, that he and his target have similar other groups within the hotel. Men in suits bring them to and from places, and the mc is always blindfolded when going outside. They eventually find out that the person in charge has done this before, and that they paid/gave excuses as to the mc's absence from home and school to people.

The reason the mc wears a mask is to hide their identity. Why? Bc ones the "target" knows the "Captors" identity/name then their ability to stay in this situation ends and something bad happens (I think).

Not sure if this spoils anything so be ware to read further:

Eventually the mc shows their target their face, but changes what the target has to know for the "game" to end. So instead of needing to know the name of the mc, the target has to know the reason why the mc is doing all this to her. Which she can't figure out.

Also, at some point another girl becomes involved as another target I think. Not sure about that though. Well, I think it was a game, it's been some time since I read it. Let me explain.

It revolves around a male protag/mc who was once bullied/is still bullied by a certain girl. However, one day, out for no where he gets a mysterious letter saying they have a chance to take revenge on someone. Thus, after accepting, he and his "target" are "kidnapped", taken to a certain hotel like building, where the mc wears a mask and enters a torture room type place connected to the mc's room, where he sees his "target" chained to the floor.

As time goes on, things are explained, how he is not the only person in this place, that he and his target have similar other groups within the hotel. Men in suits bring them to and from places, and the mc is always blindfolded when going outside. They eventually find out that the person in charge has done this before, and that they paid/gave excuses as to the mc's absence from home and school to people.

The reason the mc wears a mask is to hide their identity. Why? Bc ones the "target" knows the "Captors" identity/name then their ability to stay in this situation ends and something bad happens (I think).

Not sure if this spoils anything so be ware to read further:

Eventually the mc shows their target their face, but changes what the target has to know for the "game" to end. So instead of needing to know the name of the mc, the target has to know the reason why the mc is doing all this to her. Which she can't figure out.

Also, at some point another girl becomes involved as another target by the mc I think. Not sure about that though.