First: I literally just tabbed over to Inkstained, clicked on the first thing I saw (i.e. the most recent thing posted, and decided to read/review that. It happened to be yours. So it's in your best interest not to expect this quick a response to something you've posted.
Second: As someone with past experience with self-harm, this was something I didn't want to read. As soon as I realized what it was about, what was going to happen, I didn't want to read it anymore -- but I did anyway. I couldn't stop reading it. That is a testament to you, as a writer.
Third: I also happen to be someone who was involved in a serious auto accident, so I tend to be fairly critical of such accounts, perhaps unfairly so. However, I found your description of events acceptable at its worst, and this is also a testament to you.
But enough about me. From the first, your imagery sunk its hooks in me and wouldn't let me go. Your first sentence is stunning in its simplicity and its perfection. Everything about the introduction of Will's character is stunning. Your descriptions are poetic while at the same time not drifting off into the land of the overly flowery. This is good. This is also why certain bits, such as the description of the pain from cutting as "knife-like" fell groaningly flat. Having only read a few hundred words of your prose at that point, I already knew to expect better from you.
The pacing and flow of the story from seeing the accident to flashbacks of his own is quite well done. Regarding the accident itself, I'd like to caution that if he "woke up" in the hospital, that implies he lost consciousness. Typically people in a coma or semi-comatose state will not remember the event upon waking, or understand where they are or why for quite some time. This is a fairly difficult thing to convey in a story and it's understandably something you (as well as most writers) gloss over if it's detail not crucial to the story -- so I had no problem with that. But I'm not sure he'd have had the awareness immediately upon waking to have asked the question he did to the nurse, especially since most such patients are given quite a lot of psychoactive and other drugs at the hospital. I'd suggest expanding time a bit in that section, if only by reference (a few hours might not be long enough, but saying it was the next day could be fine).
The bit with the dialogue could use some work. For example, it's not necessary to drop "she asked" when you've ended a quote with a question mark. The question mark literally says that the speaker is asking something, and it's unnecessary to tell the reader who asked the question when there are only two people involved. Additionally, see if you can unpack some of those adjectives and dialogue tags. A word like "bluntly," to pull one example, may be unnecessary entirely, but if you want to add a cue to the reader that your speaker is changing his tone, consider indicating a change in body language (he stiffens, he leans forward, etc.) to show the reader his bluntness rather than simply telling them this was how he said what he said. The other problem with adverbs describing a manner of speech after the fact is that they pull the attentive reader out of the story, forcing them to read the line again in the way you've described. Better to indicate this before hand so they know how the words are being said and don't have to re-tune. Another little bit I'd mention there -- you write:
Keahi arched one eyebrow. “Yours?” she inquired, her melodic voice rising and falling rhythmically in pitch.
Perhaps it's possible for these sort of vocal acrobatics to be rendered in a single syllable, but to my mind (and ear) this description of Keahi's voice would be better placed after a line in which she'd spoken several words, if not a full sentence. It's virtually impossible to say a single word with a single syllable "rhythmically."
Overall, this was a beautiful and gripping read. Thank you for sharing it.