A surprise! Youku just released the character design PV on YouTube for An He Zhuan (暗河传), or their translated title, Legend of Assassin.
An He Zhuan is a prequel novel of SNGX and as of this writing, the novel is 214 chapters long and about 443,600 words. It is a work in progress though currently on a break. The author admitted that it's already much longer than he'd originally planned because it was only supposed to be a side story. The story is set about 9 years prior to the start of SNGX and centers around the assassins of the Hidden River.
The novel is currently free to read on 8kana.
Summary of story (translated from the donghua page):
Hidden River, the most secretive assassins organisation in the martial world. Comprising the three Houses, Su, Xie and Mu, the highest-ranking person in charge was called the Patriarch. The Patriarch was poisoned and his life was on the brink. When the various powers in the three Houses heard the news, they decided to mutiny. Su Muyu, leader of the Patriarch's personal guards, the Spider Shadows, brought in Bai Hehuai, the genius doctor from Medicine King Valley to cure the Patriarch. At the same time, he had to repel the killers sent to assassinate the Patriarch and protect him. Meanwhile, his closest friend in the Hidden River, Su Changhe, represented the Su House and joined the conspiracy to assassinate the Patriarch.
(Note: this summary, and likely the animation, covers only the first arc of the novel which is the first 68 chapters.)
Here is the PV:
0:12 - "No one has ever escaped from the Hidden River"
0:18 - The Patriarch (predecessor of Su Changhe)
0:22 - Bai Hehuai
0:25 - Su Muyu
0:30 - Su Changhe
0:35 - Members of Mu House (from l to r): Mu Yinzhe, Mu Bai, Mu Qingyang
0:39 - Members of Xie House (from l to r): Xie Changze, Xie Fanhua, Xie Jingke
0:44 - Members of Su House (from l to r): Su Hongxi, Su Changhe, Su Ziyi
0:46 - The Earthly Branches and Twelve Signs (地支十二肖)
Spoilery notes:
Bai Hehuai is the genius doctor from the Medicine King Valley.
Su Muyu and Su Change needs no introduction.
Mu Yinzhe is unnamed in the novel, from what I remember (but it's been a while). Mu Bai is the son of the present head of Mu House. Mu Qingyang is trained in Daoist arts and idolises Zhao Yuzhen.
Xie Changze and Xie Jingke are among the first to appear in the novel but have very little importance afterwards. Xie Fanhua is a high-ranking member of Xie House.
Su Hongxi and Su Ziyi appeared in SNGX but were cut out of the donghua. Glad to see their return!
The twelve Earthly Branches, together with Kui (Su Muyu), form the Spider Shadow Group. They do not follow their Houses and take on new codenames, named after the twelve signs.
Mu Yumo is one of the twelve - Maotu (the rabbit) and is shown 5th from the left (dressed in purple). She's very attracted to Tang Lianyue, who doesn't reciprocate.
The author personally confirmed that Tang Lianyue appears in this show and has a much more satisfactory character design than in SNGX. In his words, "...no wonder Mu Yumo is smitten by him..." Heheh.