Bungubox is a stationary store located in Shizuoka which opened in 2012. See below for a list of LE Sailor fountain pens KA-KU had released/announced as of August 18th, 2018. (Note: This list is possibly not complete.)
幸せの黄色い万年筆—Yellow Fountain Pen of Happiness
Date: April 2010
Type: Profit Standard
Limited to 30
The cap ring says “I wish you a lot of happiness”.