Hi Raf, I took a look at Japanese film festivals but there is not much fitting ones. There is only one for international documentaries.

Yamagata International Documentary Film Festival 2025: October 9–16, 2025
Call for Entry https://www.yidff.jp/2025/entry/25entry-e.html

Crypto conferences may be an option too. But I didn't find call for films.

As I see your list, submitting Water Direct to art & environment related festivals is a good idea. Those are not Japanese ones but I can recommend definitely Als Electronica Festival in Austria, where I lived. They have digital humanity category for the annual competition. It will be open early next year. For Austrian art events, @elmirabear definitely knows well.
https://ars.electronica.art/prix/en/digitalhumanity/

Chaos Computer Congress may be a place to showcase Water Direct. It's a historical international hackers' meetup in Germany. Once I visited it in 2017, a documentary how Edward Snowden escaped to Russia was screened. Unfortunately I couldn't find their call for the event.
https://events.ccc.de/en/congress/

Talking about similar art + digital + hacker events, Node Festival (Frankfurt), Transmediale (Berlin) can be an options too.

Last but not least, there is a documentary festival DOK Leipzig in where I live, Leipzig Germany :)
https://www.dok-leipzig.de/en/news/call-for-films-2024

Good luck and I look forward to taking my family and friends to show Water Direct!