If you go to the Caritas Japan page and donate via the Aid-to-Japan link, that is where it goes.
I donated and followed up with a question, got this answer:
quote
Hello XXXXX,
Thank you for your email and for your donation.
Be assured that if you donated via the Support our work in Japan link that the donation will be designated for that purpose.
I see every donation after it is processed so I will ensure that it is attributed to the Caritas Japan appeal.
Warm wishes,
Nigel Wallace
unquote
Thanks