The Apparition series has a drastically different "feel" compared to the rest of the MBU. It is visually distinctive, with a heavy (horror) noir-theme (unlike MBU's post-apoc sci-fi), with strong, bold blacks taking pace as primary colors (unlike most "greyscale" works). Red accents are also used prominently to highlight Kuchisake-onna's inhuman features (and the blood. Plus the glow).

In crossovers with the MBU series, Apparition characters carry the "colors" of their setting with them. In shared panels with MBU characters, there will often be a color gradient from the strong blacks of the Apparition series towards the primarily sepia-toned MBU comics. The overall visual effect gives an impression as though the Apparitions are corrupting the MBU-verse by their sheer presence alone, with Kuchisake-onna having the strongest "influence". Or at least, the "corruption" effects extends to their immediate surroundings that happens to "overlap" with the world in MBU (and doesn't appear to be permanent, hopefully).

So, kinda like a localized reality-warping effect, "subtly" hinted to the readers by the visual medium. Of course this is just me speculating and might not be intended by the author, but for now I will probably keep the series tagged under copyright:original (except for X-overs with MBU, where it gets both). Once more comics get uploaded, I will likely tag the Apparition characters with the "_(ishiyumi)" qualifier instead of "_(Mechanical_Buddy_Universe)".

This also helps keeps the surprise intact when the MBU characters suddenly run into an Apparition. Tags might be a bit spoilerly otherwise.

...Though, with all that said, Kuchisake-onna herself does have a very strong connection with one of the MBU chars, so I might reconsider this decision later on. Shouldn't be too hard to retag then anyway. (shouldn't exceed twenty posts, if it's necessary)