"They are the finest warriors and the perfect guardians of our Emperor."
Thiên Tử Binh - The Emperor Guards. Serve as the Honour Guards of the Emperor from Lý-Trần Dynasties and Imperial Guards of Thăng Long, the Capital of Đại Việt Empire. They answer to no one but only the Emperor. Similar to Praetorian Guard of Rome Empire, except that they not kill their own Emperor. They are specific hand pick from the army and noble family of the Empire. Only the badass among the badasses and most loyal to the Emperor can become an Emperor Guard.
When they been chose, they will enter a brutal training they ever have in their life. Then they will shaved head, get the tattoo "Thiên Tử Binh - 天子兵" on their head (f#*% you China for destroy our ancient text) and finally fully become an Emperor Guard.
"Their presence on the battlefield is always a guarantee of the victory."
We have not much document record about their activity (one again, f#*% you China for burn our text and document). But from what little remain, we know that through out their exist, they has bring many glory to the Empire and never fail in their job as the guardians of the Emperor, except... one time only. In late Trần Dynasty when the Champa king feel boring, he start to say "f#*% you" to Đại Việt and start playing Viking game near our border. The Emperor is very angry and start a huge campaign ever happen in Việt Nam history (at least until many dynasties late), marching into the southern land.
"You fought bravely without fear. But that... is not the matter anymore."
Just has a few victory turn our Emperor become an arrogant asshole who listen to no one except his big ego. And like we can easy predict, his ego lead him and his great army into an ambush lead by the Great Warrior King ever exist in Champa history, Che Bunga the Red King. The Emperor been killed, his great army been crush and destroy. And the Emperor Guards been shame forever. Follow this event, is what we know as the Age of Shame for the Emperor Guards until the day they disband.