Japan giving a security guarantee to Taiwan would be major news!

In reality no such thing happened and one YouTube video of a handful of protestors doesn’t make it so.

What she did say is that a Chinese attack on Taiwan _could_ clearly become an existential threat to Japan. Note that key word _could_

Which… of course it could!

Japan hosts multiple US military bases. If it developed into an armed conflict between the US and China then it’s exceedingly likely that Japan would be attacked. Think Chinese missiles aimed At Yokosuka, just south of Tokyo.

Not only that but Japan and China have multiple territorial disputes. It’s not hard to imagine China deciding to go all in and settle those as well.