The man in this card's artwork also appears in the artwork of "Invalidate".
This card's Japanese name also translated to "Invalid".
This card's artwork is very similar to the artwork of "Soul Charge".
Since this card was released first, it is possible that the artwork of "Soul Charge" was based on this card's one.
This card's original name was "Null and Void". On February 10th, 2017, this card received an errata in the official database, changing its name to the current one: "Muko".
This was likely to avoid an unintended interaction between this card and the "Void" archetype, which was released in Raging Tempest in the TCG on the same day.