yeah it's legit, I have a copy that came with the 4th volume when I bought it. My Japanese is definitely not perfect but I can try and explain what I think happens? (sorry in advance if there is any mistakes and also spoiler warning I guess?)
so Michi was complaining about his dad's cooking so his dad calls the twins (turns out the older is a patissier and the younger is a food coordinator) and they arrange for Shuuto (the younger twin) come over to help make food. On the day he comes it's pouring rain and he turns up soaking wet because he walked from the station (cue panels of rain-soaked collar bones). Aoto is all like "omg I can't believe you turned up" (since it was crazy raining) and Shuuto is all like "that face/expression doesn't suit you" and asks if he should go home, but then Aoto is like "no it's fine" and says Shuuto can use his shower and borrow some fresh clothes and then they can cook together. It finishes with Shuuto coming inside and there's a thought bubble (I'm not certain for sure whose it is but I think it's Shuuto's) that's saying sorry to Yuuto.
So it's pretty short but there you go. As I said earlier I'm no where near fluent in Japanese but I tried my best to explain so hopefully you are satisfied until someone can properly translate it. There is also another short extra in the same booklet about Yuuki and Matsuo that shows them a bit further into their relationship that takes place at Matsuo's place and it's also pretty cute.
Hi, thank you so much for the translation but may I ask if you know why Shuuto is saying sorry to Yuuto?
so it says something along the lines of "sorry for getting a head start, Yuu, somehow..." so I interpreted it as he's apologising for getting closer to Aoto when Yuuto isn't there
Ohh... thank you so much. So it kind of confirms that both of them like him ⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄
Thank you so much for taking the time to write this. You rock (づ￣ ³￣)づ
Someone here commented that there was a story about the twins and the omega father that was an extra in the most current volume. If that is true, could someone that has seen it describe what happened. Even if you can't read the Japanese just describe the pictures so we can get a gist of what's going on in the panels.