KuretakeFude Brush Pen in Retail Package, Fudegokochi (LS1-10S)

Is it really disporsable?

Is the ink waterproof? Does it smear on the paper when it gets wet?

How much ink does the pen carry in its barrel, 1.5 ml, 2 ml, or 3 ml?

This is listed as refillable. Is that true? I bought it, but can't fort he life of me figure out how to open it.