Bo Saixi is an incredibly beautiful woman. She wears a white and red gown with long sleeves, adorned with wrought silver. Her golden crown is shaped like a halo around her head, matching her golden scepter. Her ocean blue hair falls like water down her back and to the ground. Her clear blue eyes seem deeper than the oceans, and their depths seem to encompass the experiences of the ancients.
Bo Saixi is a calm, collected individual. She exudes a tranquil aura, and never loses her temper. In serious situations, she's rational, quick-thinking, and unfailingly responsible and kind. She defends her subordinates and territory without fear or compromise, resulting in a peaceful region with little conflict or war.
She's so devoted to protecting the world, she works endlessly to raise new warriors and leaders to protect it, even going so far as sacrificing her life to pave the way for the chosen heir of Poseidon to ascend to godhood.
Bo Saixi is the descendant of Poseidon, and was born on Sea God Island. She took on the Holy Trials, and eventually rose to the rank of High Priestess. She and Tang San's great-grandfather, Tang Chen, were very close, and she still speaks of him with great fondness. At some point in the past, she battled two Rank 99 Demi-God Douluo, Qian Daoliu and Tang Chen, simultaneously, and due to her overwhelming power when on the seas, was able to win decisively.
Bo Saixi later explained that Qian Daoliu reigned supreme in the sky, she in the sea and Tang Chen on land. Having fallen for Bo Saixi, Tang Chen and Qian Daoliu tried to woo her. She replied by declaring she'd accept the one who'd reach Godhood first. Although it might have seemed like she did not care for one over the other, Qian Daoliu and she, both divinity guardians, had attained their cultivation ranks through external means whereas Tang Chen was the only one who'd reached the 99th stage on his own and, thus, the only one able to attain godhood.
Due to his incredible pride, Tang Chen refused to return until he'd accomplished his goal. Bo Saixi waited in vain, never knowing he'd become corrupted by the dark power of the god whose position he'd tried to inherit.
Bo Saixi first appears to the Shrek Seven Devils after Tang San is revealed as the fated Son of the Nine Stars, and given a trial from the Sea God. As the Sea Dragon Pillar begins to fall from the strain of testing Tang San's potential, Bo Saixi apparates to the area to stop it in midair with sheer power, and reverses time to repair the holy pillar.
The Seven Children of the Sea God gather at Ou Ya's pillar, along with Bo Saixi. She orders them to help him with all their hearts, as he is the jewel of their generation. She inwardly muses that a war is coming, between Angel, Asura, and Sea - the most terrible war era on the continent thus far. She begins preparations to give Tang San, the Son of the Nine Stars, the best chance at success possible.
She orders the Sea Ghost Douluo to oversee surveillance on Spirit Hall, and ordered no living souls could enter within 800 nautical miles of the island. She then oversees Xiao Wu's Trial ceremony, to everyone's protest. The Sea Fantasy Douluo imprisons them in an infinite suspension technique, but Tang San is able to take a step forward despite this, and actually break it moments later. She explains Xiao Wu's First Red Level Trial is not actually a serious danger in itself, but that she would live and die according to the results of Tang San's Trial instead.
After hearing Tang San's name, she asks if he's related to Tang Chen. After hearing he's Tang San's great-grandfather, she muses that time passes so quickly, and asks if he's still doing well. Tang San admits he doesn't know, as Tang Chen left the clan ages ago, leaving behind nothing but legends and whispers. Bo Saixi smiles at the news, saying he's at least still living free, and nothing in this world could tie him down.
After telling the Trial takers to never think of failure, as the fate of the island rests on their success, Bo Saixi leaves.
Later, Bo Saixi gives advice to the Shrek Seven Devils, and guards them throughout their Trials. She, along with the Seven Pillars who serve her, helped Tang San absorb his 100,000 year God Ring. During the First Trial, she helps banish the Evil Eyed White Tiger who attacked Dai Mubai on the steps. She continues to help and counsel the Trial takers throughout their many challenges.
After Tang San leaves Sea God Island, and battles the Slaughter King, he discovers his opponent is actually the corrupted Tang Chen, by exposing him to the Light of the Sea God and weakening the demonic hold over his soul. Tang San defeats, and saves his grandfather, Tang Chen. Despite being fatally poisoned, Tang Chen travels to Sea God Island, spending his last three days of life with Bo Saixi.
Before Tang San began his ninth trial, the Sea God promised him he would help Tang Chen's damaged soul receive the qualification to pass onto the divine realm and accompany Bo Saixi's soul. At the end of Tang San's trials, she sacrificed her life to allow him to pass on to the final stage, and joins Tang Chen in the divine realm for eternity.