Refers to the breasts/cleavage of Mia Fey, a character from the Phoenix Wright: Ace Attorney series.
Origin:
On the GameFAQs Phoenix Wright: Ace Attorney Trials and Tribulations board, user Parakarry101 created a topic in which he imagined Phoenix asking Mia what it was like to be dead, an opportunity that was "RIGHT there in it's busty glory." (Mia is dead but is periodically channeled by her sister Maya and cousin Pearl, who are spirit mediums. Their clothes are too small for Mia, so Mia ends up showing her cleavage whenever she is channeled.) Many posters started posting "BUSTY GLORY" in capital, usually bold letters, which lead to the "BUSTY GLORY" fad.
Pearl's robes are too small to accomodate Mia's BUSTY GLORY.
