Proposal

He had always wanted to be in the fourth division, but somehow ended up becoming captain of the sixth. Perhaps that's why Isshin decides to study medicine when Urahara gives him a gigai and a chance at another life.

On his first day of medical school, he sits next to a sharp-eyed man with a lanky build and a high level of reiatsu. He's surprised when the man mutters "shinigami" under his breath, but what surprises him even more is that Ishida Ryuuken, one of the last surviving members of the Quincy clan, tolerates the presence of a shinigami at all. This fact immediately causes Isshin to hope for a long and lasting friendship with "Ryuu-kun," who almost always manages to shoot Isshin's hopes down with cold glares and unfeeling words. Despite this, both men develop a grudging respect for each other's love and dedication towards their line of work.

One day, shortly after they've both completed medical school, Isshin asks his friend (because they are friends, after all, and good ones too) how he should propose to Masaki. Ryuuken thinks for a moment, adjusts his glasses, and says, "Ask her when you're smoking. You'll look cooler that way."

Isshin takes his advice and earns Masaki's first and last compliment, as well as a warning that he'll have to stop smoking if they're ever going to get married. He stomps out his cigarette then and there and kisses Masaki full on the mouth. She smiles and promptly tells him to take a breath mint.

She also says yes.