Sailor Nano Kiwa-guru is a micro pigmented ink were as Bungbox Armor is dye based, both provide two entirely different writing experiences.
Where Armor falls within the spectrum of a typical dark black, Kiwa-guru does not. It's a dense, matte, somewhat layered black. While there are nuances to be found within the former, the latter displays more obvious characteristics.
Armor, like most Sailor inks, is a mid-range lubricating ink with good flow. Kiwa-guro is extremely lubricant. Both provide excellent writing experiences.
Armor is easy to clean out of a pen, but Kiwa-guru can be a pain due to the Nano pigments. Though, I've never had issue cleaning out either ink, I understand I'm in the minority when it comes to Kiwa-guro.
If you want a well rounded, nuanced, saturated black, Bungbox Shogun Armor is the way to go. If you want a highly lubricant ink with layered depth and a matte that dulls it's saturation--some maintenance required--, than Sailor Nano Kiwa-guro is the ink to use.
Thank you for this explanation. Finally makes sense of what I've read.