Guan Suo is based on Guan Yu's fictional third son from Romance of the Three Kingdoms. Bao Sanniang is his wife who usually appears in various Chinese operas and plays. Most notably The Story of Hua Guan Suo, a fable about how the two warriors met. Bao is also an homage to the the character Hu Sanniang from the novel Water Margin.
The characters on Cai Wanji's clothing is a passage from her real life literary works Poem of Sorrow and Anger.
Guo Huai, Xiahou Ba, Zhuge Dan and Bao Sanniang first appeared in Dynasty Warriors 3: Xtreme Legends as bodyguards. Cai Wenji debuted in Dynasty Warriors: Multi Raid 2 (the sequel to Dynasty Warriors: Strikeforce) which was never released outside of Japan.
Liu Shan was designed to appear not as strong as his father, Liu Bei. The developers did this by giving him an easier to wield rapier, mirroring his father's heavier dual swords.
Dian Wei's DLC costume, "Dian Wei with Hair", was originally an April Fools joke on the Koei Twitter.
The Battle of Hu Lao Gate references its counterpart from Dynasty Warriors 3, even referencing the infamous "Do not pursue Lu Bu" line from the third game.