#TWICE #NAYEON Birthday Wish

In the Korean comments

One comment calls the pairing “맏내와 맏내의 만남” (matnae-wa matnae-ui mannam, “a meeting of two matnae”). Other comments supply the key detail behind the joke: they identify Nayeon and Lily as the eldest members of their respective groups while emphasizing their cuteness.

What the words mean

“맏내” (matnae) is playful slang blending “맏언니” (madeonni, eldest female member) with “막내” (maknae, youngest member). Here it affectionately describes an eldest member with the cute or playful image commonly associated with a group’s youngest, so calling both women “맏내” (matnae) turns their pairing into a wordplay-driven concept.