They write these SO people who can't understand their terms of use can't use them.
You can call it kind of xenophobic or whatever, but it's true, non-japanese frequently DON'T read their ToS and break their rules because they didn't know them.
It is a simple password, thankfully, and you can probably figure it out with maybe 3 google searches. Use DEEP-L or Google Translate to read the ToS one section at a time, then once you're sure you understand the terms, translate the password hint and go from there.
(my only hint: the hiragana for the mythical creature described)