Nyu, I've been meaning to do this one for quite a while but couldn't find the time. Somme commas will be mentioned, but I will try not to tread on your sensibilities too much. ;3 Also, hope you meant what you said about encouraging constructive criticism because my reviews tend to end up containing a lot of criticism. x3 Oh, and just as a note: most of the comments are from my own subjective point of view and you are by no means obligated to agree with me on all of them. Style is a subjective thing, after all, and you're the author here. :3
Prologue: Okay, it's brief and suitably vague; both good qualities in a prologue. The chase scene opening is a classic and you've made it work for you. The only issue I have here is that part of your grammatical decisions are kind of interfering with the mood:
Okay, this is a chase/escape scene so it should have that hectic feel to it. In this context, I found the 'they were' here a bit odd. I mean sure, it's grammatically correct but in this case you could have just gone with "There were few beams of light trying to enter the forest, clearly visible in the haze"; it's basically saying the same thing but without the semi-colon speed bump. If you feel like going extreme wing with it you could also replace the first full stop with an 'as'.
No comma needed after "blur of red with it"; I'm picking on the commas in this chapter because commas can slow down a passage a lot.
Small note: how can one creature surround anyone? o.O
You could just replace the comma after "arm" and the "revealing" with a colon since you're essentially listing the insides of the arm you mentioned. Also, the double commas around "horrified" seem a bit like overpunctuating to me; you could just go with "Horrified, I continued...".
Like I said, it's a good prologue overall and certainly established my interest in finding out what the heck is going on. The first person perspective was also a good call since adds nicely to the chase feel and obscures the runner's identity even better than a third person narrative would. :3
First off, that should be "was" rather than "is" since this is a past tense narrative. Also, what about the hair is "light", precisely? It obviously can't be the color since you already stated that it was dark; so do you mean like...weight or something? o.O Either way, it's "Resemblant to" but "Reminiscent of", careful with those. :3 Also, I'm not too wild about real life references in description (Seeing as how it would be a bit of a stretch to expect some people to know what Paul McCartney's hair looks like); some kind of description of the hairstyle would have been preferable.
Style warning: you usually don't want two adjacent sentences to start with the same phrase since it does get that repetitive tone. You've already proven that you've got the vocabulary to avoid such things.
There's really no call for either comma here. Yes, yes, I know...I should cut down on the comma remarks but I just couldn't help myself on this one. xP
Jeff blinked in revelation. “Today’s the day I get my first pokemon!” Jeff thought to himself.
Okay...there's just too much Jeff in this passage. Again, to avoid a repetitive tone try to cut down to only one mention of his name per sentence, using more alternative expressions. Again, you have the vocabulary so use it. ;3
Again, you have a random splash of present tense in a past tense narrative, which isn't too cool.
Although Jeff has a posse of close friends, he has always made himself a bit of an odd man out and a lone wolf in the group. When his group of friends are laughing and playing he would always be a little bit off to the side, calmly relaxing and pondering about whatever is in his mind. They didn't seem to mind his lonerish ways, though.
If this were in a character profile it would be awesome, but in a fanfic this sort of sticks out and not really in a good way. Your narrative was nice and flowing thus far, so this chunk of description just came as a bit of a letdown to me. :\
Other than that...well, there's not much happening in this chapter but the dream thing and the mention of hospital (not to mention the twig) was enough to keep the plot hook in. Also, props for word choices and explaining the age thing. ;3
Chapter 2: Okay, I've got to admit: I didn't expect a flashback at this point, but it was a pleasant surprise and explains his habit. (Aaand acts as a dead giveaway of his starter, as if the twig wasn't enough of a hint. xD) Anyway, good to see a little life-threatening scenario to counter-balance the rather passive nature of the last chapter. It's hardly a new thing in the pokémon franchise but it was well played so I'm not complaining. ^-^ Just a small point, though:
I really don't think that the "Jeff began to think" bit is necessary here; touchy little phrases like that should be given their space. ;3
That should be 'shone' in this instance. Shined is only used when the verb is there are as a synonym for polish, e.g. "He stopped and shined his nifty gym badges".
Anyways, nice to see a little conflict introduced to the growing friendship between Jeff and Treecko (and a very realistic reaction from Tyrogue's point of view, seeing as how he - the alpha male, as Chikorita very aptly put it - was essentially being upstaged by a stranger.). Got to feel bad for Treecko at the end there, but it adds interest to the future development of their relationship. Also, does Jeff understand Tyrogue or not? Because with that last sentence it almost seemed like he comprehended the words themselves. o.O Regardless, you did a good job on this one; very revealing about their shared past without going completely overboard with it.
Chapter 4: Aww...Jeff's being all protective about Treecko this time around. Heh, those two really need to stop taking nasty hits for each other before someone loses an eye. And speaking of eyes...gawd, I loved that pokeball capture beam bit. They should really put security labels on those. xD
Chapter 5: Yeah, seconding Glajummy's bit on Kristie. Maybe you should consider relocating that description, seeing as how we now have more than one reader who forgot about it? I mean, in chapter 4 the description has sort of been crammed in just before the really big self-sacrifice scene with Treecko and Jeff so it sort of fades into the background. Personally, I would have liked to have seen a bit of tension from the side of the fresh catch (I mean, Corpish seems to be taking this very calmly. It's like he's been caught before and knows the drill. o.O), but that's just me. Love the way Treecko and Jeff argue even though they're friends and...aww, let's face it: I just love Treecko as a character. His interjections are hilarious. xD The battle scenes were well done; you kept stuck to the low level and limited movepool jazz without making it a boring slapfight, though I hope that Treecko will get his loss sometime too. :3
Chapter 6: Eww...Alan's a nakey! O=
Sorry, I just couldn't resist. Aaaanyway...win the battle and lose the girl...now that's got to sting. I don't know if I've mentioned it earlier in this review, but you really play your cliches well; as a reader I don't even notice them unless I look close. At any rate, the fight scenes are still going fine, but I've got to point out that you're brushing awfully close to the anime approach in handling Corpish and Treecko battle wise (Corpish tossing Bubblebeams and Crabhammers left and right and now Treecko's Bullet Seed). Please, pretty please don't make your battles go the way of the anime? I'd really like to see some battle style of your own design and not something from Satoshi. Other than that, it's a nice and enjoyable chapter. :3
Now to round this off with a few things about the fic in general: I have to agree that the characters are what keep this fic alive. Really, you deserve an extra pat for the most palpable effort you've put into their personalities. You should work on describing the setting a bit more, though. My main concern, however, is plot development: thus far the big incentive to come back has been to find out about the characters' histories, but obviously there's only so much of that you can do before things get repetitive. Is there anything in the way of bigger conflicts or villains on the horizon? A good, solid quest of some sort would be nice. :3
Anyways, I'm enjoying this fic thus far, so keep at it. Also, sorry for the somewhat superficial treatment that some chapters got, but if I sat down to really write my full, uncensored comments on each and every chapter you'd never see the end of it. Hope some of this was a bit clearer than mud. xD