In 1232, Joei Code (militarized Code of Law) was introduced in Nippon. History started to diverge from OTL when in 1274/81 no attack of the Mongols happened on Japan, so no "divine wind" was necessary too. The consequences of this are difficult to estimate - Buddhism, especially Zen Buddhism, stayed a bit weaker.
1311, Hojo Sadatoki died. He was the last recognizable member of the Hojo ITTL, who were the real power in Nippon behind the powerless emperor. The Kamakura peroid in Nippon didn't end in 1333. This would happen in 1370 when the Nipponese emperor broke free from the Hojo Shogun. Soon however, the Hatti family took the post of Shogun and the power again.
In 1363/64, Black Death was brought to Nippon by ships.
Since 1400, the Nipponese started copying Chinese arms (bamboo guns, cannons) - the first ones were smuggled in - and improving them.
The Nipponese Civil War took place in 1509-21, after the emperor tried to take power for himself. The war was fought with the new weapons, the Chinese bamboo guns and bronze cannons the Nipponese had improved - the samurai had become meaningless. Some of them fled to Ezo (Hokkaido).
Nipponese piracy and sea trade
The start of Nipponese piracy is dated to 1223. Since 1300 (2997, Yang Metal Rat in the Chinese calendar), the growing Nipponese piracy greatly hurt external trade of Song China. The fall of the Song and the Black Death left China unable to defend for some time, but after the rise of the Hong dynasty, in 1385 (3082, Yin Wood Ox) the first campaign against Nipponese pirates around Tungning (Taiwan) was started. In 1394 (3091, Yang Wood Dog), the Hong emperor destroyed the Nipponese pirates, sent his ships to Nippon, which had to give him proper respect. This was the first of many journeys his ships would make, to show the world that China was united and strong again. The Ryukyu Islands were annexed by China at this opportunity. Now, the waters around Nippon became peaceful, and the Nipponese started to build up their own trade empire, which was helped by the Pax Sinica.
In 1570, Nipponese ships trading with Java discovered the North coast of Australia, but weren't interested in this land, like the Chinese and Javans who came before them. 1594 (3291, Yang Wood Horse), the harbors of SE Asia were closed for Seljuk ships, so the Nipponese could fill this gap. Ironically, since ~1600 the Koreans started piracy against the Nipponese traders.