Aetherology delivered exactly what I needed, and just in the nick of time!
(Background, just to show how perfect and timely this information was:
In a (5e) game I have a magician with the Spider mentor spirit, whose long term objective is to create or draft a spider great form spirit and guide it to becoming the City Spirit of Chicago (and hence fending off the mostly rather undesirable great form spirits currently vying for that role, as outlined in the Anarchy publication Chicago Chaos). It is a cool concept -- both a predator to insects and figuratively someone who can knit things together with their 'web', and it works with Chicago's history as a transportation hub (a web or roads, tracks, and flights all centred on the city). The most likely outcome is that they die trying, but I'm letting them take a good run at it, waving hands vigorously where necessary as we have no information on how something becomes a city spirit.
Currently they were about to buy the "Favoured Pupil" quality from Forbidden Arcana, in one part for the karma savings so that they can dump all their longer term karma into this scheme, but two parts for the role play aspect of showing building a closer bond with Spider, as one step towards making all of this happen.
Yesterday was the session where the in-game date reached the point they wanted to spend the karma, so I had them get diverted to The Web when they thought they were investigating a metaplanar portal in Denver. (a powerful but not ultimate spirit "aether-web snagged them" he said, waving his hands vigorously). They are going to have to prove their mettle with some invae hunting, then, thanks to Aetherology, that there are three prime spirits in The Web. They are going to have to choose one of Warrior, Finder of Secrets, or Trickster as part of forging that closer bond. The character absolutely has aspects of all three, so the choice will be fascinating, and is FAR better than anything I'd come up with for this step.)
PS. I may raise another topic on this, but has anyone heard any rumours of whether the 'city spirit of Chicago competition' is going to get picked up in any of the main SR books, or if that is just staying as an Anarchy side plot?