This Gunpla is related to the Gundam Breaker Prologue, a derivative work from the game.
It is an original machine.
This Gunpla is a Hyaku Shiki with added settings inspired by Smoo.
The machine's name is an association with Smoo, with the addition of "Seki" as an honorific for sumo wrestlers, resulting in Hyakuseki.
The fighter's surname, Kagami Kouki, is taken from the kagami mochi (sacred rice cake) that is also celebrated at New Year's, as "kadomatsu" is thought to come from the kadomatsu (pine decorations) that are traditionally worn at New Year's.

HG Hyakuseki | アルジドノ's Gunpla works