Nobody knows that he is one of their earlier supporters.

She is his favorite dongsaeng, so does he.  So it was naturally that he wants both of them to be happy.

Since three years ago he had seen their stolen glances, he also observed their body languages when they were in the same room. Then it was fixed, he needed to make them see what others have seen for such a long time.

But then he could not do it by himself. He needed an ally, a collaborator, a partner in crime. Then he scanned all his dongsaengs, and was considering two others before his eyes laid at her.

Because he knew that she was her shoulder to cry on. Because she was her strength when she was shy. Because her confident was what she wanted her  to be alike.

Because she is the Black Pearl.

So he started talk to her more often, and found some codes to smoothen the mission. Included their 'Missed High Five" trademark. Something that only him and her know what it means.

Then they admitted to each other, and he was relieved. Because they were his favorite dongsaengs.

And because... by matching them, he found  his own match.

So nowadays, when he observes them, he will lock his eyes to her, knowing she is mirroring his action seconds ago.

Then he always thanks whoever invented the game of matching.