Pilot Iroshizuku Shin-Kai fountain pen ink is a blue black ink inspired by the deep sea.
This is one of my favourite Pilot Iroshizuku ink as well. I love how when wet it's lighter and then darkens while drying into a beautiful dark blue shade.
This ink has a good contrast against paper. I find the sheen to be very attractive as it gives gradations of shades within the strokes.
For writing and drawing purposes, this ink performs well. Highly recommended as one of the main colours for writing.
Below are direct links to the ink on Amazon.