Quick Transmigration: I Have to Play With Either the Male Lead or the Villain

Shocking! Being forced to bounce back and forth between the male lead and the villain: is it torment or a guilty pleasure?!

Having to choose between two options in every world leaves me torn!! Being the filling in the sandwich is hard, sob sob...

But! Adults don't have to choose

[Sorry, I think this is a slow-travel story? Anyway, the transmigration isn't fast, and I can't change the title for now.]