Okay so, let's start with the good,
Your artwork, flow, panel structure, speech bubbles, font choices, sound FX, all of that is verry solid and professional feeling, you could improve that stuff by maybe being more experimental with panel structure, or polishing up the artwork a bit more, but I don't think it needs that, and I think the rough art-style fits the tone that you're going for.
There are two things that I think are really shooting yourself in the foot though:
The first is the way you're presenting the series, as an arc within a set of other comics. There's nothing wrong with this approach, there are other "anthology" style series on this site, however, I think Cucumber Defense deserves it's own separate series from your gag-a-day comics (Pokemon Go from the future, and Learn some Japanese), doing separate series for your minicomics has added benefits down the line, it will make it so people can more easily find and share the stories that they want to, and it also makes it so newer series can have an easier time hitting the trending tab of the site. (Your position on trending is based on the ammount of views, likes, comments, and new subscribers, divided by your current number of subscribers at any given point, new series do not have any subscribers, and so each view, like, comment, and new subscriber is worth "more" on trending, compared to a series with lots of subscribers) When you create a new series all of your existing subscribers are notified about it, and the ones that want to continue reading your work will follow you over to the new project, giving you a somewhat clean slate of readers, that's more important once you get into the 100-1000 subs range though.
The second thing that bugs me though, is how you present information in your comic, the two side comics "What is a Kappa" and "Every Kappa" come off as kinda boring exposition dumps at best and condescending at worst, and they pop up at kinda a strange time in the comic, it breaks the pacing that you establish in the main part of the series, and distracts us from the actual story. I think it would have been a lot better if you had found a way to deliver that information inside the main story, which you do, in "Kappa learns about Kappa" and "I can be more" which I think are both pretty good, but the fact that they don't deliver much new information (because of the two info-dump episodes) makes them feel very redundant. I would take some time to figure out how you deliver vital information within the context of the main story, because the cutaways are really distracting in my oppinion.
The other thing worth noting, is it seems like a little bit of a kids-comic, which is fine, just know that a majority of readers here are like, maybe 16-20somethings? So you might have a bit of trouble growing an audience here if this is the type of stuff you plan on making, and that's fine, the stuff you're making is very high quality. I guess my point is, don't get discouraged if your readerbase doesn't grow very fast.
