Selucia is a high ranking Seanchan da'covale and so'jhin to Tuon. She is described as Tuon's "shadow," her ever-present personal bodyguard. Although the reader is never given a clear account of Selucia's abilities as a bodyguard, there are a few instances where her deadliness is hinted.
Selucia is described as being beautiful with blue eyes, gold hair, and creamy skin. Standing at average height, the left side of her scalp is shaved and she appears to be in her mid-forties.
Selucia spent the first twenty-five years of her life training to be nursemaid and bodyguard to the Seanchan royalty and was offered as a cradle gift to Tuon when she was born. She was responsible for disciplining Tuon. Upon Tuon's sixteenth birthday, Tuon pardoned Selucia for any punishments given and offered her one hundred gold thrones for each one, as was tradition. Tuon also gave Selucia a choice of service and was greatly pleased when she chose to be her chief maid and shadow, which meant turning her back on power and authority. Tuon only ever had to have Selucia punished twice, and Tuon regretted it as much as Selucia did.
She accompanied Tuon when she traveled to Ebou Dar from Tanchico and was present almost everywhere the Daughter of the Nine Moons went. When Mat Cauthon had Tuon prisoner and was about to leave the Tarasin Palace, Selucia arrived and pleaded with Mat not to kidnap her mistress. Once Mat vows that Tuon will not be harmed, Selucia agrees to go along, with a vow to kill Mat should her mistress be harmed.
She acts like the mother hen to Tuon when Mat "comes a-calling" and seems to dislike Mat as well for his apparent lack of respect for Tuon's social rank and it's likely she does not consider his romantic interest in Tuon proper for one so far below Tuon. Mat uses her as part of his tactics when he is trying to court Tuon. When coming to visit Tuon, he will bring her a present, but instead will give it to Selucia.
Traveling with the Band
After the skirmish with the Darkfriends in Maderin, Mat, Tuon, and the rest of their group decide to leave Luca's show. While riding through Altara they meet up with the Band of the Red Hand and begin to travel with them. Furyk Karede enters the Band's camp to escort Tuon back to Ebou Dar. Selucia goes with her.
She now acts as Tuon's Voice and warns King Beslan Mitsobar not to cause a revolt against the Seanchan. She again acts as Tuon's Voice when Tuon meets with the Dragon Reborn. She is with Fortuona when Melitene brings her Suffa, the former Amyrlin Seat, who shows Fortuona and those gathered around her how to Travel. Fortuona decrees that all damane are to learn the weave in preparation for a full-scale attack on the White Tower using Traveling to transport the army there.
By the time of Tarmon Gai'don, no offensive against the White Tower has taken place, and Selucia serves as Fortuona's Voice and Truthspeaker, as well as bodyguard, watching over her actually unused bed chambers. After nearly killing Mat, who comes to Ebou Dar wanting a bargain for the Last Battle, Selucia points the way to Tuon.
Selecia is present when Rand appears at the Tarasin Gardens. She is shocked when Rand makes the garden around them bloom with life, even though he is shielded. She continues to stay by Tuon's side; when Gray Men attacked, Selucia was injured but recovered.
There are a few hints as to Selucia's deadliness; she appears deceptively round and docile, but is supposed to be trained as a bodyguard.
The first hint of her deadliness is when she takes a position between the two Sul'dam when she discovers Mat and his entourage over a bound Tuon near the end of Winter's Heart. She places a hand on each of the sul'dam's necks - presumably to disable the most deadly threat should things take a turn for the worse.
Another hint, in Knife of Dreams, is when she moves to Mat as he's about to free three Aes Sedai that she has leashed with the a'dam on Tuon's orders. She pretends fear, hands outstretched towards him as she approaches him, presumably intending to surprise him and maximize her chances of disabling him, but Tuon calls her sharply to heel.
A final hint is after Mat, Thom, Tuon, and Selucia encounter the mob trying to assassinate Tuon, when Mat turned to see why Tuon had not run away. On the street were half a dozen dead men, and Thom with less wounds than him. It seems likely that Selucia took part in that battle, as she was injured as well as Thom. As Mat approached, Thom and Selucia had this exchange:
"And what might you be trying to forget?"
"I can't recall."
—Thomdril Merrilin and Selucia
It seems that Thom saw Selucia fight, and is willing to keep her skills a secret from Mat.
Once Tuon becomes Fortuona and Empress, Selucia takes up residence in her bed chambers as a fraud, while Tuon sleeps in different locations. She surprises and nearly shoots Mat once he comes looking for Tuon in preparation for the Last Battle.