Seems likely that Takaichi has given Taiwan a Japanese security guarantee. [1] This may be a quid pro quo.
Japan can't even sell arms to Taiwan right now. Even starting selling arms would be a huge change, let alone a mutual defensive pact.
It's extremely hard to change the constitution of Japan. It's the only constitution that has never been revised since WWII. LDP has been pushing this agenda for decades and nothing really happened.
It’s easy to ignore or work around it though, just like it routinely happens for every other constitution in the world.
The process to amend the constitution of Japan [0]:
1. two thirds of the house
2. two thirds of the senate
3. referendum
LDP just won the house. IF all LDP house representatives agreed with Takaichi then she could pass the first stage. Only two left!
[0]: https://ja.wikipedia.org/wiki/%E6%97%A5%E6%9C%AC%E5%9B%BD%E6...
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.
Or defending taiwan can be PR'd into a self-defending message.
She just won a super majority in the legislature that allows her to change the constitution.