The Disappearance of Osomatsu-san

Here's how it goes!

-Hideo is apparently a soul with no body of his own, hence he was able to stay in a body without a "natural" soul. This refers to Choro's soul, which isn't really his, but a piece of Kamimatsu's.

-Osomatsu calls for Choro, who excitedly skips to him and asks him what he needs. Osomatsu asks about Hideo.

-Choro cocks his head and simply says "He's been with me for as long as I remember!", baffling Osomatsu. Choro resumes his bothering of Kara.

-After purchasing dinner, the group decide to head out and wait for Ichi's limo to fetch them. However, across the street, they see a familiar figure.

-Osomatsu sees Choromatsu Matsuno, one of his little brothers, staring at him with tears welling up in his eyes.

...

Arc 9

-Osomatsu and Choromatsu, upon seeing each other, scream in unison and run up to hug each other tightly, with Osomatsu repeatedly promising never to leave them alone again. However, these dumbasses forget that they're in the middle of the street and nearly get run over, if not for Todo tackling them both to the ground.

-The rest run up to them, with Todo helping Osomatsu and Choromatsu up. Osomatsu excitedly introduces Choromatsu to the rest of the alts.

-Choromatsu's reactions; he waits for Kara to say something painful, but is pleasantly surprised that Kara is the most normal out of the group. Todo introduces himself as quick as possible, and immediately turns away, which Choromatsu notices and assumes he's just really shy. Ichi, as he's levelheaded, does a formal introduction, something that intimidates him a bit. Jyushi excitedly says hi and flaps his sleeves around, which Choromatsu finds familiar.

-He remembers Jyushimatsu, as well as the others, and suddenly interrupts as he "has something important to say".

-Before he can say it, however, Choro, who is pouting, interrupts Choromatsu and whines that he wasn't able to get his turn. Osomatsu ruffles Choro's hair and reassures him that they're all ears. Choro proceeds to introduce himself in his typical "Akatsuka Nightingale" manner, which gives Choromatsu goosebumps as it gives him a Karamatsu vibe.

-After his introduction, Osomatsu immediately asks Choromatsu what was the important news. Choromatsu then informs Osomatsu that Oso managed to open a "dimensional portal" temporarily, something of which was to easily send Osomatsu back into the other dimension. However, the machine, which is the phone Choromatsu and the others used to communicate with Osomatsu, malfunctioned and Choromatsu was sent to this dimension.

-Choromatsu remembers that the other four were transported as well.

-Osomatsu then asks Choromatsu what was the point of the syringe, something he has yet to inject onto Ichi, Jyushi, and Choro.

-Choromatsu explains that, in order to keep the dimensional hole stable, Osomatsu needed a presence similar to his to co-exist with him, as to create a stable bridge between the alternate dimension and his dimension. With only Kara and Todo sharing that presence, the hole was too unstable.

-The syringe's purpose was to give the alternates the memories of the Matsus in order for them to be surrounded with the same aura as Osomatsu's. Granted, it could have worked for anyone else, as long as they had counterparts in Osomatsu's dimension. However, with Osomatsu's strong connection with his brothers, Dekapan concluded that even just the six of them could keep the portal stable.

-Todo asks if the Matsus are in their dimension. Choromatsu nods, and explains that they split up in order to look for Osomatsu easier. He leads them to the park from several arcs ago (where Osomatsu, Kara, Todo, and Jyushi played in the snow), and says that they agreed to meet up there later.