Hanko Field in bank transaction form but no hanko?

Recently I moved my main bank account to Rakuten Bank (楽天銀行) and in the process of moving my bills there I found one of these on an automatic bank transfer form:

There is a field where you should stamp the seal you have registered for your bank account.

But, how does this work with an online-only bank? I don’t have a seal registered with my bank account at Rakuten Bank (楽天銀行).

After some research I found the answer in Rakuten’s FAQs

納税者、納付義務者などの欄に押印欄がある場合は、お客さまのお手持ちのご印鑑を押印ください。
口座名義人の欄のお届印は、個人口座、個人ビジネス口座の場合は、お届印がありませんので、口座振替依頼書の「届出印」の押印は必要がございません。
法人ビジネス口座の場合は、楽天銀行への届出印を必ず押印してください

So it’s actually not necessary to fill that field if you’re a individual account holder. Good to know.