Nekovalkyrja Type 33 - Wiki Article said:
The NH-33 is equipped with a pair of engineered lungs for supplying oxygen to the body. Typical rate of respiration is 8 - 10 per minute. The lungs have a lower section that stores oxygen in nodules. These can be released to prevent Hypoxia, an NH-33 possesses enough stored oxygen to hold their breath comfortably for a maximum of ten minutes under normal operation, or augment their breathing for twenty minutes in a low oxygen environment.
If we're going with what the wiki article says about the NH-33 nekovalkyrja in the group -- Yukari and Reika -- are probably going to be fine air-wise until they reach their destination if its only 200 or so meters away; assuming that they're flying relatively slow and trying to keep Kotori stable in deference to her injuries, the trip would take 5-10 minutes max -- though Suzume and Yukari seem to be putting the emphasis on speed at the moment ^_^;
...Actually Reika, like you mentioned in post, would probably start seeing issues due to having to give up air to Kotori constantly -- on second thought, probably only Yukari should have no troubles getting to the door
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Suzume and Kotori being NH-29 or some variant thereof, are probably similarly capable to NH-33 or close to it. Not sure how different from normal humans Tom and Nyton would be in this regard, seeing as they have older NH-22C Yamataian bodies. Somewhere better than human (5 minutes holding their breath?) but less capable than the nekovalkyrja, probably.
Then there is also how long it takes for brain damage to start occurring when deprived of oxygen for nekos/yamataians. Humans take roughly 5 minutes without air for brain cells to start dying off; given they're generally more robust, it would probably take longer for such damage to occur -- and it might even be repairable afterwards, given their regenerative capabilities.
Meh, random musing. I'll go along with whatever Fred/you guys decide, but just thought I'd mention these things that came to mind, anyways. Posting my RP reply now