A Japanese patent law was passed on May 25, 1871, and its provisions were described in a USPTO publication. Patents were to be granted by the "Home Office." . The fee for a patent was 5 ryō (gold coins). . We do not have examples of patents granted under this law.
Patents were granted by the Japanese government at least as early as 1885. "Invention Day is a day that Patent Monopoly Act which is the predecessor of the current Patent Law was promulgated on April 18, 1885 (year 18 of the Meiji Era) by Korekiyo Takahashi who served as the first Commissioner of the Japan Patent Office and others."
Japan procured a silk balloon from Yon in 1890 but didn't find it useful. Later they purchased a kite-balloon from Riedinger in Augsburg. They continued building their aeronautical forces and used them in the war with Russia.  In 1912 they reportedly bought a German airship, Parseval XIII.
Relevant early inventors, authors, managers, and pilots:
- Great early kite inventor Chuhachi Ninomiya (see en.wp) may not have gotten patents.
- Relevant aero inventors include Captain Kumazo Hino and perhaps his co-patentee Tomijiro Komuro, who may have worked on aircraft. Hino went to Germany for training and there is a book about it.
- Navy engineer Sanji Narahara contributed a propeller or propeller design.
- Captain Yoshitoshi Tokugawa went to France for training.
Searches for patents are possible here: https://www4.j-platpat.inpit.go.jp/eng/tokujitsu/tjkt_en/TJKT_EN_GM201_KeywordSearchCount.action I didn't get any hits and may write to their helpdesk, which had an email address, not in front of me right now.
Major new source on early Japanese aero history: Melzer, 2020
Peter has ordered a book on Hino's time in Germany. This book is relevant too but too expensive for the moment.
- U.S. Patent Office. Official Gazette of the United States Patent Office, Volume 7, issue 8, Feb 23, 1875, page 299-300
- Ryō article on en.wp
- Hildebrandt, 1908, Airships Past and Present, 172.
- w:Chuhachi Ninomiya
- w:Hino Kumazo
- w:Yoshitoshi Tokugawa