“Onii-chan”, for the record, is also hardly a “random nickname”. What do you think Japanese call their older male cousins? Not by their name alone, and not by the word for “cousin” either (従兄). It’s onii-san/chan/whatever as well. To differentiate between their real brother and their older male cousins that’s where the name comes in, but I don’t think it’s a rarity for Japanese to say “onii-chan” alone for their older male cousins if they don’t actually have a brother of their own. Especially since they obviously don’t want to reveal his name now.

There’s still perhaps the possibility that he’s her real brother, but I think there’s a higher probability of it being her cousin.

I do wonder, though, if Isako’s “brother” really went to some funny place, how she hopes to save the guy by collecting Kira-bugs. Up till now, everything that happened in the virtual world had no effects on the real world (although you could call the room Haraken was in in the previous episode an exception to this, perhaps).

I don’t think this “onii-chan” is her cousin, though. Or at least not the son of the uncle we saw in this episoe. I don’t think that a father such as him would react so calm on the message that his son could be coming back. Isako also doesn’t seem like the type of girl to just give out random nicknames. I still think that he’s her real brother, but I could be wrong with this.

Also, Daichi did not leave Hei Ku on his own, Isako banned him from the club because he didn’t manage to get the other groups’ glasses.
I think with the info Akira has gotten, the other people who are all suspicious and insulted by Isako will try to make use of her weak points as they appear (but probably not to a seriously damaging extent, unless it’s Gachagiri and co…)

As for the diary, Haraken was crying over it because it was basically Kanna’s last words the days before the accident: she realised that it was a bad thing to have argued with Haraken about the research project thing but regrets it because she wanted to stay with Haraken till the end - since she’s found out that her dad’s being transferred and she won’t be able to stay in the town much longer, and that summer (when they were both in Grade 5, i.e. a year ago) would be the last they’d spend together for now. She knows it’s silly to have believed in those urban legends about Illegals but she was convinced she had heard Chloe’s voice. So she says she’ll leave making up with Haraken to some time after she can come back, because it’s said that if you get close to an Illegal your closest friend will get cursed… She writes that she’s going to to the crossing and if she meets Chloe then she’ll say it to Haraken - that she likes him. She thinks she’ll say it to him when she returns anyway.

He sees a path drawn in her diary and insists on following it the right way in order to find more clues but Yasako tries to tell him that it’s getting late…

Oh, and if you mean the last screenshot, it’s not Isako’s brother, it’s Yonyon nii-san.

if that boy at the end is Isako’s brother, why is he sitting with Yasako?