The only experience I've had with Sailor inks so far are the Nano Black cartridges that I ordered with a High Ace Neo. It was an excellent introduction, as the Nano Black is one of the most well-behaved inks I've ever had the pleasure of using. How does the Souten fare against the likes of Pilot Iroshizuku? Pretty well, but it hasn't dethroned Kon-peki for me.
Sailor Jentle Four Seasons Souten is a bit darker and more saturated than Kon-peki, but it's still a beautiful color in its own right. It's the shade of blue that I've been looking for a long time. It seems like every time I find a nice royal blue, it dries to a much less interesting shade. Inks that dry lighter just don't make it into my rotation very often. I'm not very good at describing shades, but I'd describe this as a royal medium blue. JetPens says it's azure, and I guess that's a pretty good description as well.
You could say that Souten is the closest relative to Sailor Sky High, but I don't think it's close enough to qualify. Even so, it's a fantastic ink, and I don't think it's fair to compare the two, or to compare Souten to Kon-peki.
As I'd expect from Sailor, the ink is incredibly well-behaved. If there was one thing that annoyed me about the Nano Black, it's the fact that it dries up in the nib incredibly fast. Souten hasn't dried on the nib even when I've had the pen uncapped and unused for over 2 minutes.
On the page, Souten is smooth and wet. It still manages to dry quickly depending on what kind of paper you're using, and the finished color is still quite pleasing. Looking back through my notes, I'm always drawn to Souten before I know what it is. It has a gravitational pull of some sort.
There is slight shading in this ink, but it's not spectacular. In a wet nib, you likely won't see any shading, but it does look nice in a specialty nib. If blue inks that shade are your thing, there are others that have better shading qualities.
It's behaved very well in the pens I've tried it out in, and it has definitely found a spot in my rotation of favorite inks. Good thing, too. I've had a stretch of bad choices with blue inks, so I'm really happy to have a new go-to blue ink that doesn't look dull or ordinary.
Bleeding, feathering, and show-through aren't issues with this ink. It plays nice with all types of paper, but really shines on premium sheets like Rhodia.
Cleaning out is similar to many other inks. No hitches or problems.
When you talk about inks, you don't always feel the need to mention the bottle. The Sailor Jentle ink bottles are an exception. I love the design of this bottle. It's low and wide and appears to be squatting down to offer the ink. I love the wide cap and heft. Also, it uses a fairly standard filling reservoir that sits in the mouth of the bottle. Just turn the bottle upside down and back up, and you're ready to fill your pen from the full reservoir.
Overall, Sailor Jentle Souten is a great blue ink that I have no problem using daily. When I'm using this ink, I don't feel that it's lacking anything, which means I don't constantly want to re-ink my pen for no good reason. It's a solid, bold blue that works great and draws the writer and reader to the page.
After using this ink, I'm sure I'll be trying more from the Jentle line of inks.