Ai's grandmother is Clotho.That is, one of the Moirae (the three Fates in Greek mythology), the one who spins the thread of life.
Ai destroys the shrine that Sentarou built in her memoryat the end of the first season as a sign of forgiveness. He built it because he felt guilty for the role he had in her death, so once she'd come to terms with it, she saw no more reason for the shrine — a manifestation of Sentarou's guilt — to exist anymore, so she destroyed it.
In season 2, episode 11 ("The Distant Adjoining Room"), Ren borrowed the pink sweater he was wearing from Shizuko Amagi, the episode's client.You know, so he wouldn't have to walk-of-shame or anything like that.
Hell is Not EternalMaybe this is an attempt of mine to make the show seem just that much more cheerful, but the thing that has been keeping me wondering is that we are never really shown what Hell is actually like. We get a few sequences in Season 1 when Ai gives her clients a "taste of hell", but that was hardly very convincing. There are a few points in between the seasons that we can infer some information from:
Ai's victims get one chance to save themselves.When a contractor pulls the string, Ai's agents torment the victim in some appropriate manner, but it always seems to end the same way: they ask the victim if he has anything to say for himself. The victim always responds with defiance, and only then does Ai send him to Hell. So what happens if a victim does repent? We've never seen this happen, despite how horrific the torture sequences are (maybe they're magically designed to be scary but not interfere with the victim's honest response). But the agents almost always ask, so surely the answer makes a difference.
Ai is pissed in MitsuganaeSee above — and then notice that Ai is no longer giving most of her victims that last chance. She's also been systematically destroying the life of Mikage, a totally innocent girl. In the past, innocent children have been Ai's only weak point, but it looks like her death in Futakomori has cured her of that; she's become more bitter than ever, almost sadistic. Her agents don't seem thrilled about it, either.
Ai's existence in Mitsuganae is maintained by those who seek her.While it is true that Ai dies at the end of Futakomori, she seems to continue existing through Mitsuganae onward. This Ai may not be the same being as the Ai from the first two seasons. Even after she appeared to be gone, there were still those carrying a grudge they could not release. All this built-up hatred and bitterness maintains Ai's existence as a sort of thoughtform, In short, She exists because they want her to.
Ai doesn't accept contracts if the victim is only being targeted because they express different beliefs than the client.In episode 15 of season 2, the client's daughter tries and fails to target the representative of an opposing political party, and the show later implies that this is because someone already has a contract on him. But if that's the case, then it's probably the same with Japan's other politicians too, and most of them should be dead.
The wara-ningyo/straw doll is potentially similar to Death Note...... in the sense that its presence might or might not compel the contact/victim to pull the string eventually. Most likely, the presence of the doll simply remains a nagging fact in the back of the contact/victim's mind, like a thought they do their best to suppress but can't help but return to over and over again. Notice how several of the victims took out the dolls several times before pulling the string. Is the contact/victim is strong enough and by miracle manage to talk things over with the other party/tormentor, it can be possibly avoided (we HAVE came close to avoid having someone sent to Hell twice already in the first season- both times, the two parties talked it over. They still failed because in one case, the target was tired of life and actually asked to be sent to Hell, and in the other case, the target, for some reason, Took a Level in Jerkass all of a sudden and grabbed an Idiot Ball, demanding the string be pulled even after the contact/victim told them that the victim will go to Hell, practically minutes after target and victim reaffirmed their friendship.), but it takes a lot of effort and loads of luck. Not to mention throwing the doll away doesn't work.