Great choice for writing and sketching. The Pilot Juice Up 0.4 mm gel pens in black and violet are both pretty comfortable and practical since they are retractable. The clear top of the pen barrel displays a color band when the tip is retracted. They are both reasonably smooth considering their small tip size. They are refillable, for you can unscrew the entire color grip area from the pen barrel.

The gel ink is fairly waterproof and smudge resistant. After allowing it to dry, the pen sketch can be smudged only slightly when rubbing the ink outlines with light-colored watercolor brush pens. If you don't mind the effect of some light gray washes, it is still possible to color a gel ink sketch with watercolors.

Smaller than your average American fine point pen, this 0.4 mm tip size is perfectly suited for tiny sketches and writing in small print. The "synergy" tip grants you great precision while still feeling strong enough to withstand my normal drawing pressure.

Many pens with such a small tip usually are a bit scratchy. This isn't.
If you are searching for a smooth writing with a small thickness this is the pen you should go for.
I have a few 0.3 mm and 0.4 mm pens of different brands. The Pilot Juice Up is the smoothest one.

If you're attempting to upgrade from the original Pilot Juice, you might not want to. Juice Up's ink is a tad bit lighter and thinner than the original 0.38 Pilot Juice pen. What I liked about the original was that the grip was really close to the tip, which makes it easier for me since I hold pens a specific way where my ring finger rubs super close to the tip.

I bought an orange Juice Up Pen along with this black one. For this pen (and not the orange one) I tend to get skips every time I start drawing with it. Nothing major, it tends to flow pretty well after one or two strokes, but if I leave it unused for a period of time and start with it again, it can be an issue. I like the design of the pen though, and once I get it going it's a real pleasure to use.

my favorite pens for years

doesn't gum up, writes smoothly and reliably, and looks elegant.