David Jackson wrote:
I went to Barnes and Nobles last night, thinking I wasnt gunna find anything on Aikido, but there is a whole martial arts section and I found books on Aikido, the spiritual side, training books, etc. there were some samurai books, Bushido, Five Rings, etc.
Barnes and Noble has stock copies of Yagyu Munenori's "The Sword and the Mind" which is paired in at least one edition with Takuan's letter to Munenori on the immovable mind (fudoshin). These are must reading, and give a really excellent sense of the embodiment of spirituality in the physical practice and the means of pursuing it - especially fudoshin and katsu jinken (life-giving sword).
These should be read closely with O-Sensei's Doka, especially those on water and fire and on the mythological sword of Susanowo, Kusanagi no tsurugi (whose chief magical attribute was to control the direction of wind (i.e.- ki), thus, enabling him to control a consuming fire and drive his opponent away.)