Yugi Tsukasa/Relationships

Background
(Note: The following information contains a brief summary but may include major spoilers.)

Little is known about Tsukasa's past, but it is prevalently known that he loves Amane so far as to address him affectionately every time they meet. He recalls the expression when Amane killed him his favorite expression, to which he lovingly remarks every time the expression of fear passes along Amane's face.

However, as a supernatural, he has little rationality about keeping balance or committing his actions. He believes supernaturals should be however they want, even going forth to making Mitsuba become stronger by forcing him to eat No.3's heart. His main role is to grant the wishes of the dead, and unlike Hanako-kun, he is adamant about granting them his way. This was exemplified when Minamoto Kou brought out Mitsuba Sousuke's real wish of getting to stay with his friends, to which Tsukasa signals Nanamine Sakura to change Mitsuba's rumor to the Bent-Neck Boy at the School Entrance. He then orders Mitsuba to break Kou's neck so he would stay with him as a friend. The same case has happened with Shijima Mei, where he brought Shijima and Nene to the past where Shijima witnessed her human self lying on the hospital bed. With the wish of killing her so she wouldn't have to exist as a School Mystery, Nene stops her but Tsukasa doesn't intervene after that. It is unknown where he had amassed power that surpasses that of Hanako-kun's abilities, but due to his cruel methods of using it, several are wary of his unexpected intentions.

Similar to Hanako-kun's and Nene's situation, his human assistant is Sakura, but he holds a great deal of affection for her. He doesn't refrain from hugging or clinging to her, to which Sakura refers to him as more like a cat.

Yugi Amane
Tsukasa is Hanako's younger twin brother and the person he killed.

While Hanako feels considerable guilt over killing him, Tsukasa doesn't seem to bear any ill will towards his brother for it, though he doesn't hesitate to use it as leverage to manipulate the latter. He's always eager to meet up with Hanako, greeting him with huge smiles and hugs. He tells Hanako he loves him and asks to play together just like they used to. They have both been shown to react negatively to others interrupting their reunions. It is implied in the story and theorised by fans that Tsukasa abused Hanako.

The twins seem to have been close since they were young and often did activities together, such as watching TV and going to festivals. They are shown to be holding hands in a commemorative photo taken upon entering junior high.

As supernaturals, Hanako and Tsukasa have opposing beliefs - Hanako maintains the correct relationships between humans and supernaturals, while Tsukasa thinks they should just be however they want. In a conversation with Nene, Tsukasa describes themselves as being polar opposites and compares their current relationship to that of rivals or arch-nemeses.

Nanamine Sakura
Sakura made a contract with Tsukasa and has become bound to him; similar to Nene with Hanako. She treats him like a little child and would become exasperated if he does anything unnecessarily cruel. Despite this, she cannot disobey his wishes and still aids him in altering the supernatural's rumors. She acts as his assistant, broadcasting his altered rumors to the student body. When conversing with Nene about him, Sakura says that Tsukasa never listens to her, his actions make no sense, and he has no sense of personal space.

She then says that there is nothing she can do about it and that she decided to think of him more as a cat than a person.

Tsukasa seems to hold some respect for Sakura and will alter his actions to a certain degree once reprimanded by her. This is shown when she advised him to be nicer to ladies. When it was time for him to knock out Nene, he refrained from slamming her to the ground, opting for a less-violent method.

Hyuuga Natsuhiko
The two of them don't get along well except when it comes to following Sakura's commands or having to work together (eg. In the Tea Party Arc where Natsuhiko asks Nene out before Tsukasa dumps water on her from behind).

Mitsuba Sousuke
Sometime after his death, Mitsuba made a wish to Tsukasa to not be forgotten by people, however, the wish was too unclear for him to be able to make anything but a weak supernatural form for Mitsuba, which he then used to haunt the school lockers in order to speak to his schoolmates.

After Mitsuba's real wish was drawn out thanks to his involvement with Kou, Tsukasa took advantage of the vagueness of the wish and twisted the rumors about him, turning him into "The Bent-Neck Boy at the School Entrance". This altered, monstrous form is more powerful but has also lost the humanity that Mitsuba once had.

In the Mirror Hell Arc, it was revealed that Tsukasa had created Mitsuba using an amalgamation of body parts he found as well as part of his original soul. This newly formed "Mitsuba" has the same personality but does not retain any of the original's memory. Tsukasa then gifted him with a brand new scarf that is dark brown in color. Tsukasa appeared later to save Mitsuba when he was in danger from Number 3. He also pressured Mitsuba into consuming Number 3's heart in order to gain power, trying to force it down his throat at one point. He seems to view Mitsuba's new power with child-like fascination, attempting to rope him into fighting Hanako three times.

Yashiro Nene
It is unsure of what Tsukasa actually thinks of Nene, but more so, she's an obstacle against his goals. In the Tea Party arc where they kidnap Nene and drown her within the boundary, their relationship can be described as minor teasing when Tsukasa pretends to eat her in fish form or makes advances when she says she hasn't kissed Amane. However, in the Hell of Mirrors arc, when Nene attempted to stop Tsukasa from forcing Mitsuba to eat No.3's heart, he nearly forces her onto the floor before picking her up, saying girls should be treated nicely before apologizing.