As per with chapter 2.5 (which was translated by stride, who does the unofficial video series translations), this was an extra chapter posted around January 2024 on Otsuji's (this manga's artist) Twitter account.
This seemingly only ever happened with earlier chapters; as far as I can find, only chapters 2, 4 and 5 got this treatment.
There were some
other extras posted on Otsuji's twitter account, but those ended up being added to the end of each volume as the colored pages you can see at the end of each volume extras. Other times, Otsuji uploaded fanart of the webseries, referencing arcs that were currently ongoing, for example. Not stuff that had anything to do with manga, in any case; I won't be uploading them.
otherwise, there's gonna be so many twitter extra chapters that shiretto's chapter list is gonna start looking a whole lot like bokuyaba's kekw
There's also a few extra illustrations related to announcements of volume reprints, volume sale count milestones, etc. I won't be posting them since there's nothing really of value in them; if you're interested, go see Otsuji's twitter for the extra illustrations. I hope it doesn't seem like I'm closing my eyes and throwing darts at a board full of Otsuji's twitter posts to decide which ones I translate and which ones I don't, even though that is exactly what I'm doing
I'm not sure why it's noted as "fan art" (seemingly all of these twitter extras are noted as that); it's probably because it's not officially licensed, or otherwise it's not written by the writer who (i believe) also writes for the video series, instead being written by Otsuji themselves. Still seems weird to me
As an extra TL note, Riko-tya refers to "my favorite youtuber" as "my Oshi" (押し) originally; which means "favorite" but can have multiple senses, whether it refers to favorite real person/content creator or favorite fictional character... etc. I've opted to change it to Youtuber for reading flow (as it's clear Soshina, mentioned in chapter 4 proper, is who they're talking about, and he's a youtuber), since Oshi doesn't have perfect translations. ("Stan" is close, but it falls short in many ways)
Raws here