In the manga, while mentioned at various times, Keitaro is not shown with a dairy until HINATA 018. A Journey of Sorrow and Youth, where he starts a new journal while enroute to Kyoto, following his failure to get into Tokyo University once again.
- During her tenor as manager of Hinata Inn in her brother's absence, Kanako Urashima perused his diary and made Naru perform the various chores she had made Keitaro perform during his first days as landlord for the dormitory.
- Naru also keeps diaries to record events in her life. Usually titled by year, Keitaro accidently peeked into her diary and discovered her promise to enter Tokyo University. Later, he and Mitsune sneek into her room using Stealth Suits to peek into her diary and work out what she was feeling after Keitaro had professed his love for her.
- Shinobu Maehara also keeps a picture journal (as seen in HINATA 039. Kiss Me Senpai). However, often times she tends to write events that did not happen.
- Keisuke Urashima possessed a bad memory and used diaries and journals to help remember events and times. It was with these journals that Haruka Urashima was able to deduce who Moe was and where she came from.