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Did notnknownabout this. Definitely a sister trope. "Collapse" sounds unintentional though whereas sitting is with intent so maybe a separate article when people do not fall into it from standing.nl Even if the end result looks the same the process is key.
https://kaykayyay.wordpress.com/2012/08/04/the-w-sitting-position/
https://tvtropes.org/pmwiki/posts.php?discussion=13444039910A90466700&page=1
https://www.zerochan.net/Wariza
Has obviously been much discussion of this. This in particular looks informative:
https://danbooru.donmai.us/wiki_pages/16993
I figure Wariza Sitting would be a good name.
I don't think it would make much of a difference for the trope if the character collapses into position or is sitting like this from the start of the scene.
Recent example: http://sunny-days.wikia.com/wiki/Sunny
This has shown up in western animation too but is more common in anime. Seen rarely in real life because most people lack the flexibility. A kneeling person sits between their feet instead of on top of them. Either requires the knees to deform laterally or else requires internal (medial) rotation of the femur in the hip socket.
Do we have tropes covering postures like these? The trope identifier must be eyepatch girl in Sayonara, Zetsubou-Sensei when she hurts her finger. They exaggerate it to the point her feet come off the ground and that is the injury she should be concerned with.