Middle name not on Koseki but on passport

Our son was born in the US (to Japanese parents), and now applying for his first JP passport. On his koseki he does not have a middle name, but on his US passport and other paperwork, he does. Looks like Japanese passport can have lastName firstName (firstName middleName) to include middle names not on the JP passport

From the consulate website:

姓：SUZUKI

名：JUNKO(JUNKO ASHLEY)

1. Would including his middle name like this on his JP Passport cause any problems?
2. would not including it cause any problems? Thank you in advance.