The protagonist or a love interest of the protagonist enters into a physical relationship with a third party and comes to prefer the third party over time, consequently either cheating or breaking up the original coupling. If the protagonist is the one doing the seducing, use 'Netori' instead. If there's no evolution from unwillingness to infatuation, use 'Adultery' instead.
Castle of Black Iron novel is a popular light novel covering Sci-fi, Comedy and Xuanhuan genres. Written by the Author Drunk Tiger. The latest chapter has been translated on the panda-novel platform and can be read directly for free.