>>513299058
>>513299121
are you idiot? it is in official site of jr
rail company also say to ask first the person behind before recline to prevent trouble
read this

Q
How can I avoid problems with people behind me when using a recliner?
A
When using a recliner, if you suddenly fold it down, you may startle the passengers behind you, or if you fold it down too deeply, some passengers may feel uncomfortable due to a sense of pressure. We ask for your cooperation in checking with the person behind you.

https://www.jrhokkaido.co.jp/faq/qa0173.html