You can reserve the book if the Reserve button is shown in ”Number of reservation field section in the OPAC search result.
(Login with THERS account is required.)
Ask the holding library for any problem, such as the Reserve button dose not appeared.
<Guide Sheet: 6-2E Reserve Books that are Currently on Loan>
https://www.nul.nagoya-u.ac.jp/guide/gsheets/6-2-e.pdf