Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
Amane was abused by Tsukasa in the past
In the flashback in Chapter 13, it was revealed that Amane often came to school covered in bruises, and when Tsuchigomori, his teacher back then, asked him what was wrong, he refused to reveal a single thing, saying he was fine. He even said that he would forgive his abuser and was okay with whatever was being done to him. Had it been a normal bully, there wouldn't have been any reason for Amane to cover for him, implying that the person who was abusing him was someone he deeply cared for. Moreover, Amane has more reason to feel responsible for taking care of Tsukasa - considering what we know about his personality combined with cultural standards about looking out for your younger siblings (even with twins, the older twin still gets the title of older brother/sister). There are some other hints as well:- When Tsukasa appears in chapter 16, Hanako loses his cool completely, and is clearly very shaken and quite terrified. Not to mention, whenever his murder of Tsukasa is brought up, he completely drops his Stepford Smiler persona.
- The trivia on Tsukasa's wiki page says this:
- He likes Amane.
- His favorite snack is Amane.
- His latest concern is Amane.
- What he wants for Christmas is Amane.
- His preferred type is Amane.
- All of the above points, though they may seem funny at first glance, raise a LOT of red flags regarding the Yugi twins' backstory.
- In chapters 37/38 Nene gets sent back in time during the festival. There, she meets a young Amane, alone in the festival. He says that he had come to the festival with his brother, but his brother left him alone and that he 'gets violent if you try to stop him'. The 'violent' part here definitely has something to do with Tsukasa's rather creepy behaviour and his No Sense of Personal Space.
- Tsukasa in general is shown to be a very manipulative and sadistic person, and his treatment of Mitsuba is evidence for that. Then there's his dialogue in chapter 20, which, again raises a lot of questions regarding what happened between Amane and Tsukasa in the past:Tsukasa: Because I like it. The look on people’s faces when they decide to stop holding back. Yours was really good too, Amane. Back when you killed me.
Hanako's Yorishiro is Tsukasa
The yorishiro has been described as the 'most prized possession of a mystery'. For Yako it was the pair of scissors that Misaki used for cutting her hair; for Tsuchigomori, it is the lunar rock that a young Amane gave him. And both of them had black seals on them which are quite similar to the black seal on Tsukasa's right temple.- It is implied that Hanako deeply regrets his murder of Tsukasa; moreover, in the past, the twins seemed very close to each other, further implying that Hanako actually loved his brother, and therefore, there is a possibility of Tsukasa being his 'most prized possession'.
Yashiro will become the 8th Mystery
It was revealed in chapter 27 that Yashiro is destined to die within the next year. As we've seen with Hanako, he died when he was a kid and became the 7th mystery, i.e. 'Hanako-san of the Toilet', similarly, Yashiro is probably going to die, just as it is in her fate, and then become the 8th mystery.- There's a line in the anime's OP that could be foreshadowing this where they're counting to 7 but accidentally count to 8, and then there's the line "Wait, there's no eight". The first kanji in Yashiro's name means eight.
Mitsuba's death was due to suicide, not any accident
Just pure speculation based on the scars on the back of his neck. The scars could be implying that he tried to hang himself.
- Jossed. Mitsuba died due to a car crash. The impact broke his neck, leaving the scar.
Tsukasa is actually the embodiment Hanako's hopes and dreams
Who "Tsukasa" is isn't his own being. Rather, he's a version of Hanako that split from the original "body" when Hanako died. Since it's implied that Hanako may have died by suicide, it would make sense that "Tsukasa" would casually make reference to being killed by Hanako. We know that Hanako has/had a twin brother named Tsukasa, so how can "Tsukasa" be anything but the brother? My explanation for that is simple: The real Tsukasa is still alive and well and the Tsukasa we all concluded was the brother is really just all of Hanako's dreams from when he was still alive.
- While Tsukasa is in fact dead (or trapped in the Red Mansion), it's still possible for the Tsukasa we know isn't really Hanako's actual brother.
The Tsukasa that Amane killed is the dark entity in the Red House
- "Tsukasa" has a thing for granting wishes...gruesomely.
- The real Tsukasa is good, innocent, and kind to his brother. "Tsukasa" is twisted.
- As 4-year-old Tsukasa would bring in new sacrifices, whatever existed beneath the house started to imitate his voice.
