Relaxing in the bar one evening, Gento is surprised to receive a call from his old friend Yoshiki Kamiwazumi. Yoshiki is need of urgent assistance, and fortunately, Gento knows just who might be able to help him- CRI. In short order, Najica is briefed on the situation; up until recently, Yoshiki was working for Dr Ren, the scientist who originally created the Humaritts. A while ago, Ren and her Humaritts disappeared; over time, most of the Humaritts have shown up and been retrieved by Najica, but Ren herself is still out there somewhere. If Najica and Lila can bring Yoshiki to safety, he may be able to reveal Ren’s current location, but as Majima reveals, that is not the only purpose of the mission. Yoshiki is also travelling with his wife Serina, who is no ordinary woman. She is a Humaritt, and as per usual, Najica and Lila must bring her back to Gento.
Najica and Lila soon set off to find this unusual couple, only to run into a group of dead Humarion (a simplistic kind of Humaritt) assassins. With no time to investigate, the duo press on, finally catching up with Yoshiki and Serina aboard a train. As the two agents introduce themselves and check Serina’s Humaritt serial Number (Triple H), Serina is amused at the way Lila perfectly copies Najica movements, but Yoshiki and Najica are more focused on business, and send the Humaritts away so that they can have a word in private.
Naturally, Najica is a little surprised as to how a human and a Humaritt came to be married, but Yoshiki is quick to fill her in on their story. When Serina was originally created as a nurse or aide type Humaritt, Yoshiki was assigned to train her, but in time the pair developed deeper feelings for each other. Dr Ren was never happy with their relationship, and when she decided to retrain Serina with new protocols, the couple knew that they had to get away. After hearing his story, Najica asks him about the destroyed Humarion squadron, but Yoshiki tells her that he didn’t kill them, and neither did Serina- he has taught her to respect life, not end it.
In another compartment, Serina is playing games with Lila. The Humaritt is interested in the advanced learning capabilities of ‘Triple Z’, as well as her feelings for her master. Even as they talk however, a fresh squadron of Humarion assassins skydive onto the roof of the train. Both Humaritts detect their landing, but before Lila can investigate, Serina hands her a puzzle and tells her to remain in the compartment until she has solved it.
Leaving Lila behind, Serina heads up to the roof, where she immediately transforms from demure and gentle wife into a vicious warrior. Using a retractable double bladed sword, she easily takes down the assassins, but when she turns to go back inside, she sees that Lila has followed- the other Humaritt has already solved the puzzle. Serina quickly instructs Lila not to tell Yoshiki what she has seen- her husband must not know of her actions.
Meanwhile, more assassins head straight for Yoshiki’s compartment, but fortunately, Najica is easily able to shoot them down. As Lila and Serina return to the compartment, however, the remaining assassins attach a bomb to the underside of the carriage before decoupling it from the rest of the train. Realising what is going on, Najica and the others manage to leap off the train just as it explodes.
Najica and the others continue on through the snow on foot, but the cold weather and hard going soon take their toll, with Yoshiki being the first to tire. Although Serina wants to press on, Najica decides that it would be best for them to take a break, and the group breaks into a nearby lodge to rest up. Once there, Yoshiki and Serina collect wood to start a much needed fire, whilst Lila quickly fills Najica in on the truth about Serina.
Unaware that another squadron of Humarions is already on its way, Lila and Serina take a shower together, whilst Najica and Yoshiki talk some more. Yoshiki has sensed that Najica continually maintains her distance from Lila, and wonders whether she simply dislikes Humaritts. Continuing, Yoshiki explains that Humaritts come to mirror the hearts of their masters, and that the only real difference between them and humans is that the Humaritts are more sincere. In his opinion, a human who does not permit herself to feel is more artificial than a Humaritt.
As Lila and Serina return from their shower, the Humarions make their next move, firing on the lodge with rocket launchers. As the place collapses, Najica and the others are thrown in all directions, and Yoshiki is knocked unconscious. Enraged, Serina charges into the assassins, swiftly destroying them all with her double bladed sword as ‘punishment’ for hurting her husband.
On hearing that Yoshiki is fine, Serina sinks to the ground in relief, only to be attacked from behind by another assassin. Fortunately, Najica is on hand to shoot down the assassin, but the CRI agent does not want Serina’s thanks. Taking the Humaritt to the top of a waterfall for a private talk, she explains that part of her mission is to bring Serina back to Gento- she cannot let her stay with Yoshiki. Serina declares that she would rather fight than give herself up, but Najica is ready for this. Gripping a sword taken from one of the assassins, Najica orders Lila to remain at the bottom of the waterfall whilst she and Serina do battle.
With her double-bladed sword, Serina is fast and deadly, and it is all Najica can do to defend herself against the Humaritt’s swift attacks. Seeing that Najica is in trouble, Lila ignores her orders to stay behind, and heads to the top of the waterfall, gun in hand. As Lila approaches, Najica repeatedly orders her to stay back, and the Humaritt hesitantly stops.
Pressing her attack, Serina manages to knock Najica’s sword out of her hands. Drawing a length of fine wire, Najica uses it to ensnare Serina’s blade before it can plunge into her body, and with no small amount of effort, she manages to use the wire to throw Serina to the ground. Leaping into the air, Najica uses the wire to lasso her own sword and return it to her hand.
As Serina rises and launches another attack, Najica stands her ground, trying to figure out which side the Humaritt will attack from. To Najica’s surprise, Serina breaks her sword into two single blades, and rushes Najica in a double sided attack- and as Najica tries to dodge, she loses her footing and slips over. Now that she is unable to evade Serina’s blades, it seems that Najica is finished, but at the last moment, a revived Yoshiki throws himself in front of her. As Serina tries to pull up, she leaves herself open to attack, and two shots are all it takes to bring her down.
Some time later, Najica and the others finally make it to the end of the line, where Gento is waiting for them. Standing over his unconscious wife, Yoshiki admits that, deep down, he suspected that Serina was attacking their enemies and hiding it from him- he just didn’t want to consciously accept it. Turning to Gento, he hands over a device containing the information the other man wanted- Yoshiki himself will remain with Serina. Gento cannot believe that Yoshiki could really have such deep feelings for an artificial life form, but not even Najica will stick up for Gento’s point of view- as she points out, Yoshiki is free to do as he pleases.
Their mission complete, Najica and Lila accept a lift home with Gento, but as Lila sits in the back of the car, she cannot help feeling confused. Najica is her master, but although Lila loves her deeply, she has realised that she doesn’t understand her at all…