On Dazai, his heartrate, The Book, BEAST, and metanarratives (or: how we may or may not already know how it all ends)

Have you noticed that in the opening of season 4, Dazai is the only one who is shown to mouth along to the lyrics? Specifically, he mouths along to the last part of the line that goes something along the lines of "The context in which my soul beats, turn it into a heartbeat" (魂が打つ文脈、鼓動に変えてしまえよ (source)).

This is interesting, because as Ango established in episode 11, Dazai has been communicating with the outside world by adjusting his heartrate to encode deciphered messages. And i hate this plot point with a passion, hated it when it came up in the manga and still hate it after the latest episode, so i will cope by doing the following in this 3k word essay (which i wrote in about 5 hours on the day i have an actual real-world deadline):

Trying to figure out 1) what this skill of Dazai implies about his character and role in the overall story, and 2) how this implication is supported by the lyrics of the opening theme, "True Story" by SCREEN MODE, and 3) how this opening suggests a more intricate connection between BEAST and the main timeline, and 4) what all of this means for the current arc, the overall story, and the author(s).