One of the more curious relationships to emerge in the latest arc is between Ryuuken and Kurosaki Isshin, Ichigo's father. A high-level Quincy and an ex-Shinigami captain* are two types who wouldn't normally have anything to do with one another. Ryuuken and Isshin, however, while not exactly friends, seem fairly comfortable together. To the extent that Ryuuken is comfortable to be around, that is.

After Uryuu skips Ryuuken's training room to save Orihime with Ichigo and Sado, Isshin in Shinigami form pays Ryuuken a visit (Chapter 241). Ryuuken asks him how he got in, a little coldly Isshin thinks, but he doesn't tell him to get out. Rather, he's surprised to see that Isshin has his powers back, although he pointedly comments that Isshin's Shinigami form makes him ill. He isn't hostile, though, just his normal aloof self. For his part, Isshin seems used to Ryuuken's attitude and doesn't take it personally. Isshin makes himself right at home, sitting on the floor while Ryuuken chain smokes. They talk about being terrible parents. It's like two worn-out warriors randomly running into one another years later in a seedy bar, drinking cheap beer and wondering about the kids these days. It raises questions.

Not an ounce of their history has been revealed yet; speculation abounds. Shinigami Isshin himself is an enigma that wants explaining. Isshin has been comic relief for most of the series so far, a lovable and enthusiastic parent who is something of an embarrassment to his son. It isn't until Chapter 186 that Isshin makes his Shinigami appearance, and it comes straight out of nowhere. He shows a different dimension from the Isshin we've known so far. He's a competent and serious fighter, one who appears to be in league with Urahara. It'll be interesting to see how his past with Ryuuken ties into this, and how it will connect them to Ichigo and Uryuu's affairs.

* Okay okay, not confirmed yet, but he does wear a captain’s cape-thingy.