The entire sad story of Jacob, Penny Blake's Chinese valet, a Nice Guy through and through, who only ever harmed one person, to prevent even greater harm from befalling another, and ended up suffering and being killed for it.
Leary's backstory - the more details come to light, the easier it is to see why he's such an angry, bitter prick in the present day.
The reveal that Chao has a daughter with a white woman but refuses to let her call him "Papa" to protect her.
Mai Ling tells the story of her abuse at the hands of a warlord to a bunch of white women, though it's unclear how much is true and how much is her exaggerating for effect.
Li Yong's grief after killing Kong Pak and his rage at Mai Ling for starting the purge that caused it.
Young Jun giving his father a Mercy Kill rather than forcing him to live as a senile old man. Even worse because Ah Sahm is partially at fault for what happened to Father Jun. Ah Sahm was angered at some mobsters executing a Chinese servant boy and attacked them, causing Father Jun to be injured.
The final fight between Ah Sahm, Young Jun, and Hong as Ah Sahm finally turns against the Hop Wei for good.