It isn't irrelevant. Actually we see why Sunbae is an ass, the role of the friend who was spineless bad not a bad person, the previous relationship of Sunbae that was actually his true love. We found out what happened with the Baker's first love and his past. And the motivation of the sister who was indeed mistreated all of her life (funny Asian culture... The power-leader grandma puts aside the granddaughter because she is female (really grandma? )) due to her gender, but in the end manage to get into power. And she was not an evil person, since she speak honestly to her brother and explained to him than unless they strive for power in their family they would not be free
The story of the main couple is the first 40 chapters( too short actually). The rest are pretty much irrelevance