Link:

https://meiji-revolution.com/shonan-yokoi-351

https://history-men.com/yokoi-shonan/

http://www.caguya.co.jp/blog_hoiku/archives/2010/09/post_1709.html

http://www.city.kumamoto.jp/common/UploadFileDsp.aspx?c_id=5&id=2078&sub_id=2&flid=11205