The weather in Yamanose on November 29th, 1986 is how Ryo Hazuki refers to the day his father was murdered.
He doesn't even mention his father to anyone but Ine-san and Fuku-san. When anyone else brings up "the day it rained", he insists he's okay - before immediately demanding clues for his quest for revenge. His sights are fixed so firmly on revenge - on Lan Di, then sailors, then the Chi You Men, then Hong Kong and beyond - that his father fades away behind the anger, only taken out to be used as a key to unlock otherwise closed doors on the road to vengeance.
After Hazuki-sensei is killed, he only appears twice, in semi-secret flashbacks triggered when you inspect a bowl of carrots or the cherry tree outside the dojo. It's not long before the only person still thinking about Iwao Hazuki and what he might have wanted is Ine-san. He'd have wanted you to take over the dojo, she insisits. She's probably right.
But every step Ryo takes after he wakes up, three days after the rain, takes him away from the spot where his father died. Away from the places and people that might force him to accept and move on from his loss. Every discovery, each clue about Iwao's past - the mysterious key in a desk drawer, the basement behind a hidden door and all the artifacts in it - should give Ryo pause, cause him to consider who his father used to be, and who he decided to become. At the very least, it should surprise him.
But any curiosity is burned away by the need to move forward, to move away from the loss and the responsibility he's been left with. Every attempt by Fuku-san, Ine-san or Nozomi to get through to Ryo is either twisted to help his need to run away or regarded as a hurdle to be overcome.
And what's he going to accomplish, in the end? We're probably never going to find out, at this point - the saga ends in a cave in China, with Ryo really no closer to the answers - or the revenge - he was looking for.