WMG / Misa

Misa will live for hundreds of years, and possibly become a shinigami.

"By manipulating the death of a human that has influence over another human's life, that human's original life span can sometimes be lengthened. If a god of death intentionally does the above manipulation to effectively lengthen a human's life span, the god of death will die, but even if a human does the same, the human will not die."

If taken a certain way, it can be interpreted as the human gaining whatever life the shinigami had collected. If the shinigami had less life than that remaining to the human, the human dies of a heart attack at the original time of death, why the Note says "sometimes." Misa would, barring lethal accidents, slowly become more and more like a shinigami after the original duration of her lifespan. She has had two shinigami obliterate themselves to save her life (one indirectly), and is a prime candidate for becoming a new shinigami, or at least an undying.

• Jossed by way of How To Read 13: she dies the next Valentine's Day following the Yellow Box showdown. However, I did crunch the numbers, and Misa wound up increasing her overall lifespan by a considerable amount of time despite taking the Shinigami Eyes twice - possibly even because of it, on account of Gelus' and Rem's sacrifices.
  • The manga and anime versions of Misa may have offed themselves but the live action one didn't. So the theory could still work, just only in the live action continuity.
  • Perhaps Ryuk used the Death Note on her just to send her to the Shinigami Realm to mess with Light.

Misa is actually a fiendish confidence trickster and serial killer.

Misa is Really 700 Years Old, and her behavior is really Obfuscating Stupidity to cover up her true Magnificent Bastard personality and fool shinigami into falling in love with her and sacrificing themselves one after another. Gelus and Rem are just the latest in her inconceivably huge list of victims.

When Misa commited suicide, she became reincarnated shortly after.

She was given too much lifespan after Rem sacrificed herself to save her life, so when she killed herself, that extra life she had was used to reincarnate herself. Gelus doesn't count because Misa halved her lifespan twice before she gained Rem's lifespan. But then again, Gelus may have had a lot of lifespan in him.

• She is reincarnated in a different anime and has a good life.

Misa didn't commit suicide at the end of the anime

She just happened to be wearing gothic loli and wanted to see the city…Yeah. That's sounds good. She still dies one year later

Misa's hair color is really black.

Whenever Light is being especially evil, his eyes and hair turn red, when L is being especially good, his eyes and hair turn blue, and when Matsuda is sneaking into the Yotsuba building, his eyes and hair turn yellow, making him look blonde. You could just assume this was his personal color, or you could say that he becomes blonde when he's doing something stupid. Misa seems to be Japanese, so maybe her hair isn't dyed. Her hair is really black. It's just that she's in stupid mode all the time, so it appears blonde.

• Early on in the anime, she publicly disguised herself with eyeglasses and brown hair, which could be her natural hair color.

Misa was pregnant when Light died

It would explain why she waited an entire year to kill herself, and not on the Valentine's Day right after Light's death. That child ended up going to Wammy's House and years later would become a successor to Near.

• That kind of assumes Light ever stops working long enough to having sex with her (and he’d also have to become interested in girls). They have separate beds in their apartment after all.

Misa must have been killed by a Death Note

As noted above, she would have received all the life that Gelus and Rem had taken, including L's, and unless L was fated to have a diet-induced heart attack at 30 that alone should have given her a full life. But she committed suicide a year after Light's death. Which leaves the question of who did it: Light, Kiyone and Near would all have motive and opportunity but the Death Note only goes up to 24 days so that eliminates the first two, which would beg the question of whether Near would kill someone that long after just to clear up loose ends. On the other hand Ryuk might have remembered her on Valentine's Day and decided to come back and kill her, or some random shinigami spotted her lifespan and decided to take it.

Misa Amane isn't a full-blooded Japanese.

Perhaps her mother was of white European origin. It could explain her blonde hair, which seems to be natural rather than dyed.

Had Misa not be Driven to Suicide, she would've become a shinigami.

One of the lesser know rules of the Death Note is that it can't affect anyone under 780 days or over 124 years of age. The former is a case of Even Evil Has Standards, but the latter is odd because no human should even reach that age; in real life, the oldest anyone has been documented to live is 122. And if someone could naturally live over 124 years, wouldn't they be a very attractive target for a Shinigami, especially if they're The Ageless? Perhaps this is because they have the potential to become shinigami themselves, thus keep the numbers from dropping. Misa may have quartered her lifespan, but she still had two shinigami die for her and add their lifespan. It may be more than enough that she should live unnaturally long. And given enough time, she would become the shinigami to replace Gelus or Rem. It's one of the ways they keep their number up. Even if nobody has a second life, it doesn't break that rule as they'd Ascend to a Higher Plane of Existence still alive. Of course, this doesn't mean Misa couldn't choose to end her life and avoid the process.