Missing lyrics in TODAY

[TNeilson]

Not sure if anyone has asked about it here, but it’s bugging me for years and I still haven’t figure it out.

Before TODAY goes into the chorus part, Ayu will sing a “いび” (Yee-Bee) which non of the official lyric has mentioned about, I tried to convince myself it doesn’t mean anything, just like WOW WOW YEAH YEAH in her other songs, but the more I listen to the song, the more I’m curious and certain it’s not just some meaningless words, but I just don’t know what it is.

Anyone got the answer to this?