Earlier, Rio browsed through Jeff’s Gunpla store and heard Seria talk to kids about tips for building Gunpla. After the kids left, Rio enthusiastically asked Seria to become his Gunpla master. Later, Rio and Seria went into the Gundam Metaverse Project and he commented on her unusual avatar. He then asked why she didn’t login if she had an account, but her answer trailed off. He then wondered what he should build, and she told him that Gunpla is freedom. In the present, Rio is shocked to see Mask Lady lose a Gunpla battle to Mascarilla. Back at the Gunpla store, Rio asks Seria how she can be Mask Lady and who Mascarilla is. Seria mentions the elite title of Lady Kawaguchi and explains that she once fought in pursuit of that title, along with her sister Maria. During the tournament, Seria won her match piloting a Strike Freedom Gundam, but in the next match, Maria didn’t perform as well. In a moment of desperation, she added the wings from Seria’s Strike Freedom to her Seravee Gundam II and still lost the fight. After the fight, Maria felt guilty over using the parts and losing, and Seria announced that she was withdrawing from the final match. Maria felt that Seria was looking down on her and angrily stormed out of the room. Seria explains to Rio that this was the day she gave up Gunpla and swore to never be involved with it. However, Jeff, a distant relative, convinced her to come work for him and show kids how to build Gunpla. She figured that was okay, as long as she stayed away from Gunpla Battle and the Metaverse. Rio asks Seria why she came to the Metaverse with him as Mask Lady, and she answers that she couldn’t leave him alone because he dove into the world of Gunpla with a pure heart. But Seria was too well known in Gunpla Battle, so she came up with Mask Lady as a disguise. Seria wants to distance herself from Gunpla again, but Rio thinks that doesn’t make any sense. She says she’s not worthy of being called master, but Rio still thinks of her that way. Rio worries about the situation while logged in to the Metaverse and is approached by Magee, who offers his help. Magee takes Rio to his bar and is surprised to hear that he’s Seria’s apprentice. Rio explains the story and tells Magee that he wants Maria to know how good a mentor Seria has been to him. Magee notes that Maria was a real contender for the title of Lady Kawaguchi, but Rio still wants to take her on. Magee suggests participating in a boss raid mission to get lots of experience. At home, Rio works on the Lah Gundam and thinks about Seria. Later, Rio logs in to the Metaverse and is briefed by Magee on what to expect in the boss raid. Rio takes off and ends up in an Eldora level, surrounded by Eldora Army, Eldora Brute and Eldora Hover Brute enemies. Magee and Fumina watch the battle, during which Rio starts to feel overwhelmed. Multiple enemies are destroyed from above by the Core Gundam II+, and Hiroto Kuga tells Rio he’s fighting the One-Eyes the wrong way.
Hiroto lands on the ground and destroys multiple enemies with ease, with an assist from Rio. Another wave of enemies arrives, and Hiroto comments that Rio has a good machine. They take on the next wave and clear the first field, and Hiroto asks Rio for his name. Rio is amazed by the Core Gundam II+, and Hiroto asks if he wants to join him in taking on the boss. Rio asks why Hiroto would choose a beginner like him, and Hiroto explains that he can see how well tuned the Lah Gundam is. Seria wakes up after getting text messages from Fumina stating that Rio is taking on a raid boss. Jeff tells Seria that once a master takes an apprentice, it’s their duty to be with them until the end. As waves of enemies attack, Rio hitches a ride on the Core Gundam II+’s Core Flyer mode to reach the floating temple. The temple explodes as the raid boss emerges: Vagan Gear Sid. The boss destroys the units of multiple players, and Hiroto summons the Pluto Armor to perform a core change and dock into the Plutine Gundam. Hiroto charges in and attacks Vagan Gear Sid directly, and Rio is amazed that he doesn’t even flinch in the face of such a strong enemy. Rio combines his beam naginatas and starts attacking smaller enemies so that Hiroto can focus on the boss. Vagan Gear Sid grabs onto the Plutine Gundam, but Hiroto breaks free and slices it in half. All the other enemies disappear, and Hiroto comes in first place and Rio in second. Hiroto thanks Rio for his help, but Rio humbly says he still has much to learn. Sekai Kamiki arrives in his Shin Burning Gundam and declares that he only wants to fight the strongest opponents. Fumina is annoyed that he just appeared in the battle like that, and Magee thinks he wants to fight whoever beat the raid boss. Seria joins them in her original avatar to fight the match. Rio decides to fight since the Plutine Gundam was damaged in the fight. Sekai asks Rio if he’s the champion, and Rio answers that he isn’t, but still wants to fight. Sekai accepts the challenge and immediately attacks, but Rio is able to dodge. Rio rushes in and attacks with his beam naginata, which Sekai blocks. Seria thinks back to the joy that she and Maria experienced from building Gunpla. Sekai comments that he’s impressed by how well Rio is doing, and he unleashes his ultimate move, the Enouzan. Rio loses, but tells Sekai how happy he was to fight against him. Magee tells Rio that he must’ve learned a lot, and Rio is surprised to see Seria there. She explains that there’s a large-scale battle coming soon and that Maria will definitely participate, so she wants Rio to take care of her.
The second episode offers some insight on who the mysterious Mascarilla is, and we learn that she’s actually Seria’s sister, Maria. The whole affair seems rather petty to drive such a wedge between the sisters. Rio wants to power up and confront Maria, and he happens to encounter Magee from Build Divers, who offers his help as he usually does. Rio takes on an Eldora-themed mission and runs into Re:RISE star Hiroto, along with Build Fighters Try star Sekai. It seems unlikely that such experienced players would be impressed with someone who is such a newbie, and it’s an aspect I didn’t care for in the original Build Divers. Still, it’s good to see that Hiroto is still at the top of his game and has created the Plutine Gundam (even though Pluto is no longer a full planet). Sekai’s appearance, while fitting for his personality, seems rather pointless though and was just an obvious attempt at cramming in another legacy Build series character. Even though Rio is so inexperienced, Seria decides to entrust him with fighting her sister, a master level fighter. That doesn’t seem like the right kind of story to tell when you only have three episodes.