PIECES - trigger word

There are two instances where Rethabile uses miyao's trigger word: <PIECES>, using this trigger word causes the music in the game to abruptly cut to silence and Miyao to blank out.

<music cuts> 

<Music cuts, Miyao is startled>

This is completely intentional as there is written instruction from the game's director in the game files to stop the BGM as soo as Rethabile uses the word 'pieces'

Pause BGM when Rethabile uses the word "Piece"

Miyao showing such a reaction means that this word is one of his programmed triggers, as this Miyao we see is a program, there is also proof that the music playing is diagetic to the story, as in it's actually playing for Miyao <post>, it cutting out means that there has been a glitch in his selcom.

Rethabile accidentally discovered one of Miyao's triggers during the first scene and the second time she has used it on purpose for some reason. You can see the complete change in her attitude between the two scenes. 

I. We are more than game pieces in a war -> II. We are nothing more than game pieces

It's a complete 180 switch, and as Toujirou says, As soon as you acknowledge you're just a piece, it's all over for you.

Miyao's attitude also changes throughout the story, at first he believes that he is the main character but as time goes on he accepts that he is nothing but a piece.

Another instance is when Miyao uses the word game pieces, regaining some of his hope and believing he still has agency, to move differently than he is ordered to, as soon as he says the word pieces, Rethabile appears.

She is here to talk about Cyril with him who might have some clue leading to the mastermind, which makes Miyao hopeful, but as we know Cyril gets killed and the evidence blown up, this causes Miyao to accept that he is just a piece.