Rurouni Kenshin: Haru ni Sakura
るろうに剣心 春に桜
The "Kenshin Kaden" basically refers to the last extra chapter (comes after the end of the manga and after Yahiko No Sakabatou) of Rurouni Kenshin entitled "Cherry Blossoms in the Spring Time" (Haru Ni Sakura).
It was published in the Kenshin Kaden Artbook.
Taken from The-OrO.com