Titled Cradle Planet, the tale is tagged as a novel, but is more of a short story in terms of length. Ichiro Okouchi, screenwriter for the anime, wrote it. Okouchi also contributed to series like Turn A Gundam, Azumanga Daioh, RahXephon, Code Geass, Valvrave the Liberator, Kabaneri of the Iron Fortress, Heavy Obect, Devilman Crybaby, and SK8 The Infinity. Eriko Sugita translated the Gundam Witch from Mercury prologue novel into English from its original Japanese.
The story takes place after the prologue anime episode that aired before the series premiered. You’ll need to watch it to get necessary context.
The novel begins when protagonist Suletta Mercury and her mother moved to Mercury after the events of the prologue episode. The story is written not from Suletta’s perspective, but from that of Gundam Aerial, Suletta’s mobile suit. In the series proper, Suletta often refers to Aerial as a member of her own family, and the story illustrates why. Aerial seems to be intelligent. Aerial sees Suletta as her own sister. The Gundam Witch From Mercury prologue novel details Aerial’s perspective as Suletta decides to attend the Asticassia School of Technology, despite being unaware of their mother’s plans to use her children to get revenge on those who wronged them.
Mobile Suit Gundam: The Witch from Mercury airs on various streaming services and the GundamInfo YouTube channel.