|The sanzen room at Korinji|
That being said, it is not popularly recognized in the West that koan training in Rinzai Zen is not a homogeneous thing at all. Each teaching line, in fact, transmits its own nuanced style of koan practice, flavored by the personalities and the training experiences - sometimes recorded, sometimes transmitted orally - of its past lineage holders. These transmitted styles of koan practice are called a lineage's shitsunai: literally, what takes place "within the room," that is, the sanzen or dokusan room where master and disciple encounter one another.
Generally, there are two main so-called schools of Rinzai Zen koan shitsunai: the Inzan and Takuju schools, named for Inzan Ien (d. 1814) and Takuju Kosen (d. 1833), both dharma heirs of Hakuin's student Gasan Jito (d. 1797). The different personalities of these two teachers are often said to be what makes their schools of koan practice distinct one from another. As described by Dumoulin in his Zen Buddhism: Japan, "Inzan Ien, a man of powerful naturalness, confronted and pursued his disciples, while the quiet, balanced Takuju preferred a more steady and methodical sort of progress."
Whether or not this and similar characterizations are true, we may observe that in Takuju koan practice one generally works through a series of koans from various collections, such as Mumonkan and Hekiganroku, in their textual order. In Inzan style practice, however, this is not necessarily the case: koans from many sources may be encountered in a mixed order, according to an overall scheme that addresses specific points (and sets particular traps) for the student.
Of course, since each teacher is free to assign whatever practices seem to suit the student regardless of so-called school, no absolutes may be established. Still, it is interesting to think that general trends within the two schools do in fact stem from the characters of their namesakes. Recorded in our shitsunai documents are, in fact, jakugo (capping phrases) given by Inzan and Takuju in the course of their own koan practice under Gasan; from those alone, differences can (indeed, must) be seen.
Something else not generally known in the West is that even the Inzan and Takuju schools are not homogeneous traditions. The Inzan school has at least two surviving sub-traditions, the Mino-ha and Bizen-ha. Our own shitsunai used at Korinji, and of course at Daiyuzenji in Chicago where So'zan Roshi is abbot, comes from Omori Sogen through our teacher Hosokawa Roshi. It is the style carried at Tenryu-ji and is, in fact, a mix of various traditions. Since I have trouble keeping those historical details straight in my mind, and for the benefit of our students, I will record them in the note at bottom (with thanks to Hosokawa Roshi, who made all this clear to us some years ago and whom I largely quote there).
If there are Rinzai Zen students reading this who are unclear what practice heritage their teachers carry, I would encourage them to ask and clarify the issue. The accumulated experiences - indeed, the enormous effort, sweat, and blood - of each lineage's forebears together constitute living inheritances that are extraordinarily precious. And, we should understand that these are not static or dead "curricula"; shitsunai can continue to grow and transform with the lifeblood contributed by each generation of practitioners...including our own. It is therefore good, I think, for us to start by knowing exactly to whom in the past - and in what manner - we are each deeply indebted.
Tenryu-ji's shitsunai (carried also by our teachers) is primarily the Inzan school Bizen-ha, with a little bit of Mino-ha and also some of the the Takuju style mixed in. This came about because Ryoen Genseki Roshi (d. 1918) did sanzen for seven years under Razan Roshi at Bairinji, which carries the Takuju style, before he became a student of Tekisui Giboku Roshi (d. 1899) at Tenryu-ji. One of the chief priests of Tenryu-ji also was Gasan Shotei (d. 1902); he did sanzen under Tairyu Buni (Mino-ha, at Shogen-ji Monastery) before himself becoming a student of Tekisui Roshi at Tenryu-ji. Both Ryoen Genseki and Gasan Shotei went on to become Tekisui Roshi's successors, and the shitsunai they transmitted each carries various elements from their mixed backgrounds. Gasan's lineage today is still carried at Shokoku-ji, while Ryoen's remains at Tenryu-ji.