Katrina was a very fierce and strong mermaid, who was once leader/Alpha female of her colony for many years before Ryn took her leadership. She committed suicide after refusing to rejoin Ryn's tribe stating they're not her family.
An alpha leader of the mermaid colony.
Long ago, Katrina was born into Tia's colony to an unnamed Mer-couple. However, she became orphaned when her parents were killed and Katrina was separated from her natal colony. She was subsequently found by Ryn's Colony who took her in.
For many years, she was Alpha female of the entire colony and ruled with a fierce, predatory heart.
Katrina has lighter tan skin with freckles across her face, deep violet eyes and long light-brown hair flowing down her shoulders.
Like all mermaids, her mouth has sharp fangs and a gray fishtail. But after she joins Tia's forces, she gains orange scales and lighter grey complexion.
As a mermaid, Katrina is naturally violent and aggressive. However, she also follows a strict code and feels morally obligated to uphold them when pertaining to her mermaid colony. Katrina was willing to kill Ryn out of fear, derived from her staying on land for a long period of time, which broke her strict moral code. Katrina’s murderous nature, however, got the best of her and caused her to lose her leadership position in her mermaid colony to Ryn, who bested her in combat, but spared her life, once she surrendered to her.
However, she seems to hold resentment for being stripped of her leadership and harbors a desire to return to being the "Alpha female" of their colony by battling Ryn again in a tank, with Helen, Maddie and a reluctant Ben as witnesses. Katrina is quite stubborn, but eventually learns that she must trust Ryn and her human allies in order to get what her fellow-mermaids/mermen all want: their oceanic home back. Despite Katrina’s initially-calculating and intolerant behavior, she eventually learned to work with those around her whether she liked/trusted them or not.
In season 3 she's is shown to have become more loyal and tolerant towards Ryn as her leader as shown when she turned on Tia (A blood relative of hers) to save Ryn instead of using Tia's upper hand as an opportunity to reinstate herself as leader. However, eventually she does turn sides.
Throughout the Series
After putting on the clothes she had stolen, she appears in Helen's shop, where she is intrigued by Helen's keepsakes of the things from the sea. Once she finds Ryn, she and merman Levi attempt to take her by force or kill if necessary to get Ryn to return home. She and Levi reveal their true purpose via hissing; that they are here to eradicate humans for what they had done to Donna while experimenting on her, and kill Ryn because of her attachment to the humans.
She escapes and is pursued by Dale Bishop, but manages to elude capture. Then, after she confronts Ryn, Ben, Xander, and Donna, she, along with Levi, fights against them before retreating. She then acquires some antique spears from Helen's and uses them as weapons for her fight. She then escapes into the cargo hold where she ambushes Ryn. However, her aggressiveness took hold of her, and she gets bested by Ryn and surrenders after a beating. After Donna gets shot by Xander, she helps transport her to Helen's home before Ryn tells her to return to the colony and never return, under orders that she tell the colony that Ryn is dead.
Many months later, she eventually chose to return to the land where the humans dwell, along with Levi and four others: three fellow mermaids and one merman. Accepting Ryn's help, now she is the alpha female, she and her fellow merfolk take Ben's request to dwell in the cottage of his family which his parents have not been in for a whole decade.
Still resentful of losing her role as leader to Ryn, she is more hostile than the other four who came with her. Especially towards Ryn, considering her "weak" like humans. After running off, she encounters the same gray wolf that had attacked Cami earlier, and ended up killing him in a bloody battle. She returns to the abandoned Pownall cottage, carrying the wolf's corpse on her shoulders.
Afterwards, when Ben and Maddie create a tank that serves as an emergency for the merfolk for dehydration, she discovers that Ryn is already weak from the dehydration.
She gets stabbed by Ryn's tail stinger while fighting her in the salt water tank, she later woke up and left the Marine Research Center. Xander finds her unconscious on the docks and imprisons her in one of the holds in his late father's motorboat the North Star, he interrogates her about Levi's whereabouts. She tries to escape but Xander shows her the drillship belonging to Klesco Oil that is preventing her and the rest of her people from returning home. He claims that he will help her if she helps him with his "problem."
She eventually succeeds in escaping and intends to have Levi and the other three return to the sea, where there are "no humans and no Ryn", by force if necessary. After seeing Ben's genuine assurance that he would do all in his power to save her and her kind, does she warm up to some. She then takes part in foiling Klesco Oil's plans for drilling in their home, but the plan costs them Sarge's life. She along with the others swim with him back to their home where he is given a burial. After some time, she brings Cami on a hunting trip and explores a plane wreck. When she pries open a door, she finds, to her surprise, a sickly elderly mermaid inside.
In the third season, we learn that she originally belonged to Tia's tribe.
In "Mommy and Me", she receives word from Hunter that Tia and discovers her large tribe that she has formed. Tia's tribe finds her colony in a plane wreckage and becomes surrounded. Tia communicates with her via merfolk sign language telling her that they share the same blood; they are family, Katrina chooses to side with Tia, betraying Ryn's colony altogether. Her mermaid form transitions and she now bears the same scales and wide pelvic fins as Tia's tribe. She then brings Tia's colony to the island where the surviving members of Ryn's colony took refuge in. Soon after giving them clothes, she along with the others hunt them down, only for Katrina to run in with Ryn. After a skirmish against Ryn and Hunter, Katrina was given a chance to rejoin Ryn's colony, but she refused and, taking Ryn's spear, slit her throat and died. Her corpse was last seen laid down next to the other slain members of Tia's tribe.
You're not my family (Final Words)
- She is the first female leader of a mermaid colony but loses her high-ranking status when Ryn defeats her in combat.
- She is the third mermaid to appear in the series after Donna and Ryn, respectively.
- She was the only violet-eyed mermaid in the series until Tia's arrival. That's because Katrina was born into Tia's colony.
- It is unknown how Katrina is related to Tia.
- She is named Katrina due to her constant aggression and destructive behavior, like the infamous hurricane, as Xander puts it.
- It is revealed in that she was the one who ordered Levi to kill Sean, being the Alpha female before Ryn usurped her, both on land and tank water.
- In "Mommy and Me" she makes the decision to join Tia's tribe and betray Ryn's colony. She becomes a subordinate to Tia.
- In "The Island" during her fight with Ryn, she committed suicide after refusing to join Ryn.
- Deadline — Freeform’s Mermaid Drama ‘Siren’ Gets Premiere Date, Casts Duo, Releases Clip (October 7, 2017)