Mitsuba Sousuke/Relationships

Background
Mitsuba Sousuke used to attend Kamome Academy's middle-school division before he passed away in an unspecified accident. Before his death, he had previously met Minamoto Kou. Masking his personality, Mitsuba decided to hold a passive, caring persona in order to make friends. His past reflected on the bullying of his girlish traits and cocky attitude. Unfortunately, it has left him nowhere, labelling himself as the boring background character. Thus, his soul was still attached to the middle school, often asking people if they remembered him while they were changing shoes. Kou forcibly confronted him as his two friends fled, causing Mitsuba to shudder under his intimidating approach.

Mitsuba did not remember much from his past, only that he had held a camera that was donated to the photography club. It is later seen that he was part of the photography club and often took pictures for the school albums, as noted by the pictures taken of Nene's gardening club. Nene notes that he was a boy that has won awards for his photographs, but Mitsuba rarely mentions it. Mitsuba doesn't have much attachment to any particular people in the past, only that he was standing with a family member for his entrance ceremony.

Minamoto Kou
At first, Kou and Mitsuba did not get along, as Kou finds his Mitsuba's attitude annoying and Mitsuba continuously insulted him, calling him a "Hella-Lame, Traffic-Safety-Earring Boy" and generally being rude.

However, once he finds out Mitsuba's reason behind his haunting, they quickly came to an understanding. Hearing about how Mitsuba was bullied in the past and how he tried to fake a personality to fit in better yet ending up being forgotten, either way, Kou assured him that he'd remember "Mitsuba Sousuke" as someone who's "cocky, looks like a girl, sarcastic, selfish, has an annoying voice, obsessed with his camera, goes emo sometimes, and is only fake nice", and that he only needed to be himself to make friends. It was also found out that Mitsuba used to be Kou's classmate.

When Mitsuba asked if they would have been friends if he were still alive, Kou responded that it didn't matter if he's dead and that they could still be friends. Mitsuba also took a picture of him, and when asked what photo he took, he answered that it was "something important" to him. Their time is cut short by Tsukasa, and Mitsuba dies as a ghost.

Having never made any friends in middle school, Mitsuba greatly appreciated Kou's company, and his declaration they're friends. He was able to be more genuine and display emotional vulnerability around him.

During their reunion in the Hell of Mirrors, Mitsuba did not recognize Kou due to losing his memories. He is confused, and can clearly see how hard Kou wants him to remember of what they did when the original Mitsuba was alive. By the end of the Hell of Mirrors arc, Mitsuba is left with the only source of information about his past; the gardening club photograph book (in which he was the photographer taking them).

In the Picture Perfect arc, both of their character developments evolve here, as well as their relationship, seen especially in Chapter 47 and Chapter 48. Kou and Mitsuba are first seen in Chapter 47 in the school building- Mitsuba wanting to look at the shooting stars. Kou first confronts Mitsuba about him knowing the way to get out of the fake world created by Shijima Mei but is interrupted by Mitsuba revealing his true form and using his power to present the past. He explains to Kou how he learned about his original self from when he was alive till now. It is revealed that he is envious of his past self, and how he hates the fact Kou only truly cares about the true Mitsuba rather than him—a fake. Kou denies this and is blown away by the now smashed window. Mitsuba goes on to tell Kou how much fun it was to hang out with his classmates (making cookies, cleaning the pool), and then turns to Kou. He says that he’s happy in the fake world and that Kou should be happy there too. He tells him to pretend that he’s real and that they could be happy there if he did.

He asks Kou if they could be friends again while putting on a smile and holding out a shaky hand. Kou chucks his hand away and denies him, telling him that he could never find happiness in a fake world but yet they start to fight. When they stop, Kou tells him that it’s wrong for him to want to, ”...spend the rest of your fake life, in this fake world, with your fake friends,” and how it’s wrong for him to spend his life being Mitsuba when he isn’t. Kou then says that he could make his wish come true in the real world, and it makes Mitsuba angry. He starts to cry and shove Kou, asking him with what power could he have to make that come true, and how he doesn’t understand at all. It’s then shown that Mitsuba wishes that Kou would stay by his side and how he wished the people he loved were dead, so that he wouldn’t be so alone and jealous of their lives. He says, “How could something like me be understood by a human like you!”

Kou grabs Mitsuba's hand, and tells him that in that case, he should die too, “So we can stay together forever?” Kou proceeds to fall back and jump off the building in order to stick to his word and die, but Mitsuba is quick enough to save them. By the end of this arc, it’s seen their relationship grows significantly more. Mitsuba uses his powers to keep up with what Kou and his friends are doing during the day (as seen at the epilogue and its recent chapters).

Yugi Tsukasa

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 Hell of Mirrors 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 red in color. This Mitsuba doesn't seem to be aware of the fact that he was Tsukasa's creation, or that his "original" version was once a normal human.

Mitsuba is scared of Tsukasa, as he often forces him to do things he doesn't want to, like eating Number 3's heart in order to make him a school mystery. However, having lost his memories, he sticks closely by Tsukasa, the first person he ever met. He seems to have settled in somewhat with Sakura and Tsukasa, though he still teases Mitsuba sometimes.

Yashiro Nene
Prior to the story, Mitsuba took pictures for Nene's gardening club back in middle school, but the two did not formally meet until the Hell of Mirrors arc after the disembodied hands brought her to him.

At first sight, she thought that he looked handsome and prince-like, but Mitsuba quickly shattered that impression by commenting on how fat Nene's ankles are. When he explained that he was trapped in the boundary and had asked the hands to bring him someone that could help, he quickly won Nene over by acting cute in front of her so she would help.

Later, he revealed that he does not remember anything about his former life or the cause of his death, and that's probably why the mirror boundary hadn't been able to attack him yet.

When the 3rd School Mystery's minions began attacking them and Nene was caught, he tried to save her by throwing items at her attackers, but he also ended up getting caught.

Mitsuba seems pretty fond of Nene as a senpai. He protected her from falling debris after he accidentally hit them with his new powers, and tried to impress her by exclaiming that he's gotten stronger now, even though Nene didn't really understand. When he forcefully pulled Nene, Kou, and Hanako out of the mirror boundary, he told her to keep quiet, and that they'd see each other again.

Hyuuga Natsuhiko
Mitsuba and Natsuhiko seem to be on good terms, despite the fact that Mitsuba never calls Natsuhiko by his name and doesn't want to be friends with him.

Minamoto Teru
Mitsuba first meets Teru in the Melancholy of the New No.3 Arc, only to be directed with disgust. However, Mitsuba sees a clear similarity with the person he saw in his memories, almost mistaking Teru with Kou. But before Teru could use his weapon against him, Natsuhiko saves him after proclaiming Teru was looking for a date.