I must say, well done! This is a huge imporvement from the first chapter; longer, more plotty, and definately more emotional. I think you pulled off the feeling of sorror over Sunflora's death quite well for a beginning fanfiction author. The whole flashback made the reader come to respect Sunflora just as much as Darren, but the whole time it is obvious that his Pokemon is dead... My only advice for that kind of writing, the kind that touches the reader and gets to their emotions, is to keep practicing it. Once you get the hang of it, you're only going to get better and better the more you experiement with it, and I'm pretty sure based on that chapter you've got the hang of it.
Of course, there were still a few problems, but it's nothing near the way it was last time around. Let's see...
There's still the problem of not adding new "paragraphs" for new speakers. This is easily fixed, though. Here's how this paragraph would look if written out like that:
"No, everything is not okay, my Sunflora is gone!" Darren did not mean to sound so rude, but didn't care anyways. He just wanted to see his Sunflora's yellow face again, smiling back at him. He remembered the day he found it, ten years ago.
Simple, right? Not to mention it makes the paragraph look much less clumped together and much more proper. Just remember: a new speaker calls for a new paragraph. Most writers have this problem when they begin, but it is also easy to fix.
I noticed while I was reading this that the words "the Sunkern" seemed to get a bit repetitive. While this isn't very serious per se, it's important to avoid repetition as much as possible in your writing. How, though, with something as simple as a Sunkern? Well, a lot of fanfiction writers would mix it up a bit, by using different wording that stays obvious to the reader. For instance, the words "the Sunkern" could be used once, and then in the place of that same term a sentence or two later, you could add something like "the seed Pokemon", or "the tiny yellow creature". This serves two purposes: to avoid repetition, and to add description in a more unique way than just stating something's appearance.
On that note, this whole chapter could have used a bit more description of the Pokemon. Other than Sunflora and Belossom, you didn't really describe the appearances of them. What about Sunkern's appearance? Nincanda? Gloom? Smeargle? Small words of description here and there would give the reader a better picture of the scenes and the creatures involved.
I really can't think of much else to say. You're on the right track, though, that's for sure. The "October forest" setting was beautifully described, as were things such as Sunkern's evolution. I admit to having felt a little bit like crying when I started reading that last paragraph. That's what to aim for. All writers of things like this, be them novelists or fanfiction authors, strive to make their writing as descriptive, touching, and expressive as possible. They want to hook the reader into the story in hopes of more. It's the writer's responsibility to give them more. And I'm confident that you'll only get better from here on out, with a little work at it.