Volume 4[]
When Raphtalia found Keel in Idol's dungeon, she proved her identity by reminiscing about when Sadeena saved Keel from drowning.
Volume 5[]
Just before the wave at Cal Mira Island, Raphtalia wishes that Sadeena was there to fight in the wave. She was revealed to be the best swimmer in Lurolona Village and was like a sister to Raphtalia. Naofumi admits that a swimming-type demi-human would be very useful when fighting in the water.
Volume 10[]
As Naofumi was setting up food supplies for his village, Raphtalia wishes that Sadeena was present since she a fisher and a strong fighter. She was unable to protect the village from the waves since she was deep out at sea fishing at the time.
When Naofumi and his party went to Zeltoble to free slaves that had come from Raphtalia's village, he had unknowingly met Sadeena under the stage name "Nadia." Nadia had proved to be friendly and very knowledgeable about the coliseum but was also a bit of a drunkard. As she explained the workings on the coliseum, she kept on ordering drinks for the both of them. When Naofumi learned enough for the day, he paid for the drinks and left.
After Naofumi started participating in the coliseum tournaments, the two met met again at the tavern. As before, Nadia provided advice over drinks. As they talk, Naofumi reveals that he can't get drunk which thoroughly impresses her. Nadia then takes him outside as they continue to talk until they are both ambushed by some opponent fighters. Nadia shows off her impressive combat skills as she defeats them and then warns Naofumi about further ambushes. She then professes her love for Naofumi and heavily flirts with him as she reveals that she tried to poison Naofumi with extremely potent alcohol. Naofumi immediately rejects her and she then heads out, hoping that they will meet again.
A few days later, as Naofumi, Raphtalia and Filo advance up the coliseum, they were finally scheduled to fight against Nadia. Before the fight begins, Nadia reveals that she knows that Naofumi plans to buy all of the slaves from Lurolona Village. With Naofumi's team under the effects of a curse that significantly reduces their stats, Nadia shows extreme skill in close-quarters combat, magic and tactical maneuvers. In addition, supporters in the stands paid to enhance Nadia and debuff Naofumi's team. As Naofumi's team gets knocked around by Nadia, she eventually turns into her therianthrope form. Raphtalia recognizes her and calls her by her real name - Sadeena. As they pretend fight for the spectators, Raphtalia brings Sadeena up to speed on their mission to rebuild the village. Apparently, Sadeena has also been working to buy back the villagers. After making a flashy performance, Sadeena pretends to be defeated.
At the disappointment of the coliseum spectators, Naofumi's team and Sadeena are matched up against the final opponent of the coliseum - Murder Pierrot. During the difficult fight Sadeena showed Naofumi how to cast cooperative magic together. With that magic, they were able to defeat Murder Pierrot. After the battle, they confronted the crooked merchant running the coliseum. Sadeena's debts were waived and they returned to Lurolona village with the missing villagers. Back at the village, Raphtalia and Sadeena reveal why Sadeena has been overly flirtatious with Naofumi. Apparently she's always wanted a partner who could drink more than her and Naofumi is the only person able to do it.
Volume 11[]
Back at Zeltoble, Sadeena goes with Naofumi to the slave traders. While there, Sadeena recognizes and points out Fohl from the coliseum. Naofumi decides to buy both Fohl and his sister Atla.
Back at the village, Sadeena worked on helping the villagers level up and protected the village from any attacks. Naofumi starts to become intimidated by Sadeena's advances. Eventually, he decides to have Sadeena reset her levels so that he can optimize her build to which she easily agrees. After the level reset, she starts leveling up in the ocean.
Later on, Sadeena successfully teaches Keel how to transform into her therianthrope form.
Volume 12[]
After Atla had been healed, she became obsessed with Naofumi. Sadeena tried to convince her to leave Naofumi alone but was unsuccessful. As they were talking about Atla, Gaelion played with the merged Zombie Dragon and Demon Dragon core which had previously been a part of Naofumi's armor. Sadeena tried to stop him before he swallowed the core. As the dragon runs away out of control, Sadeena correctly surmises that he had been taken over by the souls of the core he ate. She joins Naofumi on the team to track down Gaelion and protects the group while traveling. On the way there, Sadeena explains the Way of the Dragon Vein magic to Naofumi.
When they finally reached the possessed Gaelion, even Sadeena's powerful attacks were not able to pierce its skin. However, she then cast cooperated magic with Wyndia and Melty to create a giant mass of water. With her exceptional fighting skills underwater, she was able to damage the dragon. However, she stopped once Wyndia convinced her father - the zombie dragon in control to stop. Unfortunately, the demon dragon then took over Gaelion's body which then became even more powerful. As Naofumi's party attacked the demon dragon, it started a long incantation. During the time Sadeena and Naofumi cast their cooperative support magic on Atla who then proceeded to greatly damage the dragon. After Gaelion and Filo were able to escape from the Demon Dragon's body Sadeena, along with Gaelion, Atla, and Raphtalia, was finally able to perform a combo finishing move and destroyed the demon dragon.
Later on, Sadeena heads with Naofumi and a few others back to the Zeltoble coliseum for training. Eventually they had come across Itsuki who was being manipulated by Malty and had unlocked his pride series bow with a corrupted sense of justice. Sadeena helped evacuate the village children while Rishia fought with Itsuki.
Several days after the fight with Itsuki, Sadeena and Gaelion decide to personally train Naofumi in the Way of the Dragon Vein magic. To their surprise, Naofumi learns the magic quickly. Afterwards, they decide to bond together over alchohol at Sadeena's island. Sadeena tries to get Raphtalia to reveal her feelings towards Naofumi but unfortunately she passes out from drinking too much. Afterwards, Sadeena takes a more serious tone and asks Naofumi about his intentions with Raphtalia. Naofumi, still being emotionally broken from Malty's betrayal, reveals that he has no romantic intentions. Sadeena then mentions that Raphtalia is secretly royalty and if her origin country found her out they may try to kill her. As Raphtalia wakes up from her stupor, their conversation ends.
A couple of days after their conversation, Erhard had arrived with a Miko priestess outfit that Naofumi had order. When Sadeena saw Raphtalia wearing it, she immediately tried to tear the clothes. She tells Naofumi that it has special significance in Raphtalia's origin country. However, Sadeena was too late and the village was attacked by ninjas. Sadeena defends the village from the ninja until they were completely repelled. She then explains that the attackers were from Raphtalia's origin country of Q'ten Lo and that the miko dress is a symbol that she intends to take the throne.
Volume 13[]
Before heading to Q'ten Lo to stop the attacks, Sadeena gives a general overview of the country. She then joins Naofumi and the rest of the traveling group on their way to her birth country. They stop through Siltvelt since it has the only connections to Q'ten Lo however Siltvelt's obsession with the Shield Hero kept them or a while. Sadeena, along with the other party members are separated by Naofumi for most of the time. When he was assaulted by the women in the bath, they all immediately ran to rescue him but he took care of it by the time they got there. When Jaralis' group tried to poison Naofumi's party, Sadeena was one of the members who secretly noticed. Finally, when Jaralis' group tried to attack the Siltvelt leadership, Sadeena was part of the group which defended the council from the mutated demi-humans.
Back on their way to Q'ten Lo, Sadeena started to teach Raphtalia how to properly use her Vassal Katana compared to the ill-fitted sword techniques Raphtalia was using earlier. She also protected the party from Q'ten Lo's assassins. After repelling an especially large group, Sadeena jumped in the water to follow Naofumi and Raphtalia as they were being dragged into the Water Dragon's lair. As they left the underwater cave, Sadeena acted as the guide and immediately noticed that the townspeople were acting strangely. She was also fortunately able to repel the officials after Naofumi and Gaelion protected a child from a monster.
After being contact by Raluva's son, Sadeena reunited with Raluva who had helped her escape Q'ten Lo with Raphtalia's father and mother. He requests that they overthrow the current Heavenly Emperor and advisor. After agreeing, Sadeena, Naofumi's party, and the rebels attack the lighthouse which was controlling the barrier around Q'ten Lo. She attacked the leader of the lighthouse guard. Together, they were able to free the lighthouse and drop the barrier preventing the rest of Naofumi's group enter Q'ten Lo.
Volume 14[]
After a sealed orochi monster was released, Sadeena with the others fight it to save the harbor town. Together they were able to defeat the monster but they then found out that it was only a weak copy and the real body is somewhere else. After the real body was found, Sadeena turned into a massive killer whale with Naofumi's help and provided the bulk of the damage to the monster. She realized that all of the 8 regenerating heads had to be destroyed before defeating the monster so they worked together and finally defeated the Orochi.
Talking with the rebels about their current opponents, it was revealed that after Sadeena had left, her parents had another daughter to take her place as Water Dragon Miko Priestess. Later on, Sadeena has a serious discussion with Naofumi about her past and her connection with Raphtalia's parents. She reveals that she had an abusive childhood with her parents and was forced to do the dirty work for the country. Raphtalia's father was one of the only people who cared for her so she helped them escape when they were in danger.
As the revolution continued, Sadeena's sister requested single-combat with Sadeena to come to a peaceful resolution. Naofumi and Sadeena both agree to this battle. Before the battle, Sadeena's sister introduces herself as Shildina. While Shildina had oracle powers, Sadeena had years more battle experience than her so the battle began in her favor. However, Shildina used her oracle skills to copy Sadeena's abilities and then the spirit of the previous heavenly emperor. Shildina had just barely incapacitated Sadeena when her powers destabilized and she collapsed. As Shildina was starting to be taken over by Makina, Sadeena halted the possession and put the previous heavenly emperor in the Makina's place. Shildina then went to Q'ten Lo's castle to stop Makina. Sadeena and the rest of Naofumi's party followed her. Together, they were able to defeat Makina and destroy her spirit. Afterwards, Sadeena and Naofumi recruited Shildina to become a member of Naofumi's party.
Volume 15[]
After Motoyasu joined Naofumi's village, Sadeena had lent him her Water Dragon's Harpoon to copy. Later on, Sadeena was approved to be part of the core group from Naofumi's village that will fight the Phoenix.
During the fight against the Phoenix birds, Sadeena was part of the group that mainly fought the high-altitude bird that was resistant to magic. After a mysterious attacker defeated one of the birds, Sadeena along with the others desperately tried to kill both of the birds before the explosive revival occurred. Unfortunately, they were too late.
Volume 16[]
After the death of Atla, Naofumi became mentally unstable and started acting unusual towards his friends. Sadeena started counseling him and tried to correct his mindset. With her help, he started the healing process. Later on, Sadeena and Shildina took Raphtalia and Naofumi underwater level grinding for the first time. With Naofumi's help they were able to fight harder monsters and gain a large amount of experience. Sadeena reveals that she is already maxed out at level 100.
Later on, Sadeena joined the diplomatic party that was going to Faubrey to meet the remaining Vassal Weapon wielders. After Takt attacked the diplomatic group, Sadeena initially fought against Shate. They were only able to escape due to Raphtalia staying behind to cover their exit.
In the preparation to defense against Takt's invasion of the world, Sadeena recruited fighters from the Zeltoble coliseum. During the defense, Sadeena was part of the counter-attack team which directly confronted Takt. Sadeena faced Shate one-on-one for a rematch. With Naofumi's new buff skill and beast transformation assist, she was able to get revenge for her earlier defeat. In the end, they were able to defeat Takt and his harem.
Volume 17[]
As Naofumi's group prepared to travel to Glass' World, Naofumi focuses on training his village. As a result, everyone at level 100 including Sadeena get the level-breaking ceremony with Gaelion. With the ceremony, Sadeena decides to focus on agility, strength and magic. Afterwards, Sadeena and Shildina lead the leveling up efforts in the ocean. When deciding who will travel to Glass' world, Sadeena was selected due to her close relationship with Raphtalia who is over there and level-independent skills.
After traveling to Glass' world, they save Raphtalia and that world's heroes from an invading enemy Vassal Weapon wielder. Sadeena and Raphtalia then joyfully reunite. Since her level had been reset to level 1 from traveling to another world, L'Arc acquires earth crystals for her and the other party members to level up. Being jealous of Naofumi he also challenges Sadeena and Shildina but easily loses.
When Naofumi's and L'Arc's parties were teleported close to the captured Kizuna, Sadeena pretended to be a Jewel to blend in and checked the area around the nearby dragon hourglass with her sonar. When in became time to invade the underground maze, Sadeena was part of the first group to enter while concealed. She was caught in a teleportation trap that placed her in another portion of the maze. She met up with Glass and then rescued Kizuna. Immediately after, they went to help Naofumi but by that time his group had already defeated Miyaji and the other vanguards of the waves had escaped. After the victory, Naofumi uses his new Food Level power-up method to empower everyone including Sadeena.