Ishida Souken, the "First Quincy", was Ryuuken's father and both Ryuuken and Uryuu's master. Unfortunately, he was killed when the latter was very young. Gentle and wise, Souken was everything that Ryuuken was not. He encouraged Uryuu's training, even entrusting him with the Sanrei Gloves, the ultimate Quincy weapon that cost Uryuu his powers in the Soul Society. Although not necessarily a father figure, Souken was model for Uryuu and a beloved teacher.

Ryuuken's relationship with Souken, on the other hand, isn't clear. In Uryuu's memories, Ryuuken referred to him as "that old man" and told Uryuu to stay away from him. It seems that at some point, probably when Ryuuken decided to give up being a Quincy, he cut off contact with Souken.

Souken was killed by a Hollow before the series started. The Shinigami who were supposed to be keeping an eye on him arrived two hours too late to save him; he had already been dead for an hour when they finally came. Later, it is revealed that the Shinigami were bribed by Mayuri, captain of 12th Division, to arrive late so that Souken would die and Mayuri could "study" his soul. The injustice is that Souken advocated a partnership between the Quincy and the Shinigami. The Quincy were necessary, he reasoned, to handle Hollows that the Shinigami would not be able reach in time. The Shinigami refused to listen, insisting that Hollows were their problem alone. Neither of his heirs seem to share his hopes for reconciliation.