A few weeks ago, Youku YouTube channel posted a couple of shorts of 少年歌行番外篇之少年事 (Shao Nian Ge Xing Side Stories: Stories of Their Youth). To my surprise, they centered around Baili Dongjun and Ye Dingzhi and spoil a part of the SNBM story. As a prequel story, SNBM already has a spoiled ending but there are interesting events that happened in the story anyway.
Here are the two episodes. They're not subbed yet (as of this writing) but I'll summarise below with some added background from the SNBM novel. The premise is Wuxin hearing the story from Baili Dongjun even though in the novel, they never met face-to-face after Wuxin grew up. The young man in blue-green is Baili Dongjun and the other young man he's very friendly with is Ye Dingzhi (Wuxin's father).
Part 1:
Wuxin drops by a random restaurant and orders food and wine. Baili Dongjun offers better wine and tells him the name of the wine is "Too Early". The name comes from the wine's fermentation being stopped too early or it would have been a better wine. Then, he tells Wuxin a story about the Hagemon of Chu (楚霸王).
[I don't know why Baili Dongjun calls him that, but he's referring to Ye Dingzhi.]
Baili Dongjun met Ye Dingzhi the first time in Heavenly Revelations City (which he called a hateful city). They were both there to participate in an entrance exam for Jixia Academy to become the final disciple of Li Changsheng, the number one under Heaven. Lei Mengsha (Lei Wujie's father) was one of Li Changsheng's disciples and also one of Baili Dongjun's sponsors. (The other sponsor was Langya Prince Xiao Ruofeng.)
Lei Mengsha was annoyed at Baili Dongjun for riding his horse through Heavenly Revelations City (which is against the law for civilians) as he could be arrested and disqualified from the exam. Then, Baili Dongjun met Ye Dingzhi who gave him a hand. Besides the tests in the martial and literary domains, they each had to pass an additional test but the candidates were given the freedom to choose their own topic.
Baili Dongjun chose to brew wine, obviously. Ye Dingzhi chose to demonstrate his skill at roasting a whole cow. They decided their respective topics were a match made in heaven and the two became best friends in the course of the exam. The wine that Baili Dongjun brewed was "Too Early". (The wine's fermentation was stopped early because it had to be done by the end of the round of exam.)
In the final round of the exam, the two were separated but the rule was that the first to arrive at the end would become Li Changsheng's disciple. Baili Dongjun arrived first but he wanted to wait for Ye Dingzhi, who he was sure was not far behind. But Li Changsheng only wanted one disciple and asked him who he should choose. Baili Dongjun insisted that he'd be crazy if he chose only one because they were both so outstanding, but Baili Dongjun said he arrived first so he had to be the shixiong (older brother).
Meanwhile, Ye Dingzhi was running away from Fei Li (a high-ranking member of the Outerheaven Sect) who had been sent to kill/kidnap him. This was also the reason why he was separated from Baili Dongjun because he was drawing Fei Li away to let Baili Dongjun escape. Disappointed that Ye Dingzhi never arrived, Baili Dongjun recognised Li Changsheng as his shifu and not long after this, they left Heavenly Revelations City. Li Changsheng told him that the most important factor in finding a master was fate. Li Changsheng was fated to have only one more disciple (not two).
[The credits confirm that Lei Mengsha is voiced by Zhang Boheng who also voiced Lei Wujie.]
Part 2:
Baili Dongjun continues the story and says the Hagemon of Chu met someone who changed his life - a woman. After Ye Dingzhi was injured by Fei Li, he woke up in an unknown room and a lady, Yi Wenjun, nursed him back to health. He described her as the moon in Heaven who has taken a human form.
Later still, Ye Dingzhi was cultivating a demonic sword art from his master but he couldn't fight the demons in his heart. The monk who helped him to overcome his demons was Wangyou (Wuxin's shifu). Wangyou advised Ye Dingzhi to stop cultivating the sword art but Ye Dingzhi said he made her (Yi Wenjun) a promise that he'd take her to see the world and never let her be locked up in Heavenly Revelations City.
Ye Dingzhi told Wangyou he gave himself this name because he wanted to swing his sword at all under Heaven and challenge the throne of Heavenly Revelations City (which is where the 'ding' comes from). That was why he had to master this sword, and he was prepared for the consequences whether he demonised or not.
Baili Dongjun asks Wuxin what he thinks is the most frightening thing in the world. Wuxin recalls his experiences (in Season 1) and is not afraid of things that threaten his life because as long as he's strong enough, he can beat them. Baili Dongjun says that the most frightening thing in the world is a beautiful woman.
The flashback resumes. Later later still, Baili Dongjun tried to persuade Ye Dingzhi to turn back (from his demonised self) but Ye Dingzhi refused. Baili Dongjun did not want them to become enemies but Ye Dingzhi said they already were and bid farewell.
Baili Dongjun gets drunk at this point and the narration becomes unreliable. LOL. He claims that Ye Dingzhi got married with his wife and went on to lead a leisurely life of farming and raising kids. After Wuxin leaves, Baili Dongjun wakes up and says fighting and killing are the most meaningless things in the world. He only wants to tell a story to the little monk and since it's a story, it should have a good ending at the most romantic part of the story.
On Ye Dingzhi's tombstone, it says remembered by "friend Baili Dongjun and wife Yi Wenjun".
In the last flashback, Ye Dingzhi and Baili Dongjun said their goodbyes after leaving Heavenly Revelations City. Ye Dingzhi decided to head south to Nanjue and seek his master (where he learns the demonic sword arts) while Baili Dongjun headed west to Snow Moon. They hope to meet again when they have both made a name for themselves and they would still be youths.