noun
secondary couple; sub-couple
Wasei-eigo term used in media fandom to refer to a romantic pairing that is not the main couple, often in TV dramas, anime, or manga.
wasei-eigo (Japanese-coined English), from sub-couple
このドラマでは、メインカップルよりサブカップルの方が人気がある。
In this drama, the sub-couple is more popular than the main couple.
サブカップルの恋愛模様も丁寧に描かれている。
The romantic developments of the sub-couple are also carefully depicted.