Masaomi Iki (壱岐正臣 Iki Masaomi) is the older brother of Hiyori Iki.
It is also implied that there is quite a large age gap between himself and Hiyori.
It is further implied that he has been residing overseas shortly after graduating from college, which was when Hiyori was a young child. At that time, he told Hiyori that it was okay to run away if things got too hard for her, and encouraged her to do her own thing rather than becoming a doctor like their father.
Masaomi has recently returned home and now works under the alias "Kaii Sera" as an Art Director Designer for a side job. His family does not seem to have knowledge of this. It seems that his appearance has changed significantly while he was away, as his family did not immediately recognize him upon his return. His hair had grown out, and he now wears glasses. He is the only member of his family who appears to have trouble with his eyesight.
Masaomi is a man of average build. His exact height is unconfirmed, but must be greater than 173cm as he is shown to be taller than Yato. He has dark hair, presumably similarly colored to that of his sister, which is longer in the back with uneven bangs on his forehead. After returning from his time overseas, he wears rectangular, black-rimmed glasses.
He is carefree and dispassionate about his life, shown by how he doesn't wish to inherit the family business and uses art as a means to escape responsibility. He also prefers not to take big risks in his life, and just live quietly and independently. However, Masaomi seems to be quite dissatisfied with these parts of himself.
As a doctor, he is presumably of high intelligence. He is also well inclined toward art, music, and sports.
Hiyori is Masaomi's younger sister by many years. Despite being quite lackadaisical and distant from his family in most areas, he is caring toward Hiyori, shown by how he helped her study, questioned Yato's earnings when he found out they were acquainted, and guarded her when their grandmother brandished a weapon in the house. However, Hiyori is unaware of his career as an art director designer, implying there are some things that he still keeps from her.
- Sensing Creatures From Far Shore: Unlike normal humans, Masaomi can sense, hear and see the creatures from Far Shore. He inherited this ability from the maternal side of family.
Masaomi is visually introduced in chapter 53. He is first shown standing in front of Yato's graffiti as he talks on the phone with him. He is later shown from the neck-down helping Hiyori study.
He gives Yato and Yukine his business card, which identifies himself as an art director designer under the alias Kaii Sera. (It's noted that he selected this name because he thinks an artist should be called something unique and cool-sounding.) He explains that this is only a side job, and that he is not tied down to just painting, like his friend was until the "end". He gazes at a poster of Ryouichi Uno's painting, implying that the famous artist was his friend. He explains his concern over how his friend has recently been saying that he is being possessed, and asks Yato to help solve this problem for him, insulting him in the process. After he cheerfully runs off, Yukine says that he is similar to Yato in that they are both carefree people who don't think before they speak.
It is later revealed that the friend Masaomi was speaking of was a ghost who was once an artist, and was now possessing people (including Ryouichi Uno) so that she could paint. He thanks Yato and Yukine for their help. He goes on to admit that he was quite envious of the ghost, since he was very passionate, meanwhile he is living passively without any real goals. He found accuracy in her statement that what he does is not art but rather a means to escape; but he also remembers her saying that escapism could be turned into something genuine if you put in the effort. At the end of the chapter, the backside of the business card reveals that his actual name is Masaomi Iki.
In chapter 54, Masaomi calls Yato and Yukine to ask them to get more toilet paper while he's on the toilet. He then invites them into his maternal grandmother's home for tea, where they run into Hiyori. He questions how they know each other, and Hiyori says that she had Yato are just friends. Masaomi then excuses himself to give their grandmother a check up, revealing that he is a doctor. He is shocked and grabs Hiyori protectively when their grandmother attempts to shoot Yato and Yukine with a bow and arrow. He admits that he and Hiyori can both see beings of the Far Shore, and appears very excited when he learns that their family carries this ability. After Yato tells them that the black shadow outside their grandmother's home is similar to a god of death, Masaomi and Hiyori insist that their parents live with them (until their grandmother passes, though they do not specify that).