@PangTong
Actually, it's factual if you can actually somehow lower the oxygen content in the air.
https://www.quora.com/Can-inhaling-pure-nitrogen-kill-someone-instantly
If the proportions of other inert gases are high enough in comparison to the oxygen levels, it could draw out the oxygen in the blood with a single breath, leading to unconsciousness in seconds. There are documented cases of this happening in places where inert gases accumulate in high concentration compared to oxygen, like CO2 buildup in an enterable storage tanker or gases denser than air accumulating in concentration at the bottom of some area.
I believe the main point is to create air that has a very low partial pressure for oxygen, which is a mix between the air pressure and air mixture (O2 content). A low pressure environment lowers effective partial pressure and lower O2 % mixture does as well. So if Yanagi has some kind of poisoned hand that consumes oxygen as well as uses his vacuuming effect, it could seem feasible (without actually going through how it works).
Also, from my research, most helium tank supplies used to fill up balloons are mixed with air to prevent this from happening along but mostly because helium is becoming more and more rare on earth.
https://news.ycombinator.com/item?id=17870696