I wonder if it's spin-off or continuation?
if it's spin-off, is it about rudeus and his sister?(Norn)
It's canon for sure. The 7th volume in a nutshell is what Rudy does after his separation from Eris. He is basically using his adventurer name "Rudeous of the Quagmire" to get his standing up higher, so he has to accept harder quests and join with other parties (though most were all super weak compared to Rudy or the rest of Dead End). For some weird reason, the manga just forgot this was a thing so i guess now they are doing it. I am not expecting much though. Hot take, I really hate the artstyle of the Manga. The anime and LN do it so much better.
People do not seem to know but the Light Novel's 7th volume wasn't in the Web Novel. It was completely new content and thus completely skippable.
It wasn't "for some reason", it's just that they probably wanted to skip to the more important parts.
They might've just not wanted to adapt a single volume's arc too, since the previous one lasted 4 volumes and the following one about 3.
it wasn't in the original web novel but it is a important volume, the manga adapts the Light novel not the web novel so it should have been adapted, Sara, Soldat and the party rudeus was does appear again in the future and the adventure he had with them is a important part of rudeus development, he didn't just skipped it he resumed it in 3 pages as a joke, completely different from what it really is, seeing people treat rudeus depression and erectile dysfunction as a joke proves that the lack of this content affects the experience, why do you think it was added to the light novel if it hadn't a purpose?
the author himself said that he regreted to do a time skip in the original web novel and fixed it in the light novel.
and volume 7 is considered one of the best volumes of mushoku.
there is literally no reason to skip volume 7, its just a bad decision
Not once did I say it wasn't important, just that there's no reason to adapt it. Web novel seems to have done well enough on it's own so you could consider the new volumes to be more like extra content or side stories. All the volumes in which Sara, Soldat and the others appear are extras, aside from a short appearance of a party member in the actual story I think. And yeah, I don't like how they wrote it off in the manga as nothing but a joke, but the manga's a comedy while the LN isn't so just blame it on whoever decided to draw it.
Point is, yes I like this volume, yes I want it to be adapted into the anime, yes I do think it's somewhat important. Is it necessary though? No, university arc is much more important than depression arc and should definitely be prioritized.