I don't think the team would blame Gray for a death so cruelly, even if it looked like it was Gray's fault.

Nevertheless, I quite liked it. It was written well and it hits right in the feels. Good job :)

Sad : ( Well, I'm a sucker for Gray angst, and his guilt hurts a lot. It kind of makes me want to write something along similar lines, but I already have way too many projects on my plate, ha ha. Okay, so Gray was great here, especially with the guilt and how in the memory/flashback he couldn't speak even though we got to hear his thoughts of what he should have said. And I may also actually like how the team sort of blamed him at first but once the shock wore off and they got more information, they (I assume the rest of them will too, aside from Natsu) turned it around. Well, I do think it was a good little piece.

And since you asked for concrit... Okay, let me suggest a couple pointers. This is just a small thing, but you might want to consider separating your A/Ns from the story content. I personally bold them and use a line break to separate them out, but people do it different ways. It's not a big deal, just that it would make it easier to read.

My biggest grievance (if you can call it that), is with the dialogue. If you used dialogue tags then the commas at the end of the dialogue would be appropriate, but since you mainly use action beats that are totally different sentences, you need full stops at the end of your dialogue.
A couple examples:
Wrong: "I'm coming in," The loud snap of wood was unsurprising, and Gray let the splintered remains of the door topple onto him, "Hey."
Right: "I'm coming in." The loud snap of wood was unsurprising, and Gray let the splintered remains of the door topple onto him. "Hey."
Wrong:"It's not your fault, you know," Of all the things that Gray had been expecting to hear...
Right: "It's not your fault, you know." Of all the things that Gray had been expecting to hear...
Wrong: The playful jab was enough to bring about a slight smile, "Flame Brain,"
Right: The playful jab was enough to bring about a slight smile. "Flame Brain."
Etc.

I also didn't understand your reference to "cracked sniveling". The adjective doesn't make sense there (although the "flounder in his failures" part is great and I like the alliteration). Sort of something similar with "crackled reply". I think I get what you're going for, but that's a really awkward adjective to use there. Sometimes it's more effective to use a more humble, down-to-earth word instead of looking for something fancy. I mean, I love fancy descriptions and words, but if you misuse them then they become really jarring.

One other point was when in the memory/flashback Natsu tells Gray to get up so that they can go tell Makarov that they failed. The whole "dejection" bit in the next sentence helps a bit, but it seems a tad odd to me that that's what Natsu is going to say right after a girl died. Not callous exactly, but... It doesn't quite fit to me. But that's a personal preference, I'm sure.

Aside from that, I do like how you write your prose. It's descriptive and although occasionally your words meld in strange ways (see above), they sometimes mix to make beautiful descriptions. The memory/flashback was especially good at that.

And I like how Natsu came back afterwards to patch things up with Gray and help him out a little. I think the way you did it really reads as something he would do and stayed in-character. Although yeah, the actual ending wasn't my favorite XD It read like you just didn't know how to end it so you threw something together. Or like it was 3:32 a.m. and you wanted to wrap it up so you could go to sleep ; )

Anyway, I think it was a nice story. Good job : )