Finished reading volume 13 yesterday.
I'm guessing spoilers have already been posted all over anyway so I'll just write a quick summary. I'm not going to spoil tag the whole thing so just skip the post if you don't want to see them.
It picks up back at the stand-off between Aqua Current and Argon Array. They exchange some harsh words that imply there's a grudge between them (at least from Karen's side). Aqua is able to use refraction by manipulating her water coating in order to alter the trajectory of the lasers, but even the slightest graze of the lasers takes out 1/10 of her HP. Haru realizes she is just buying time so he can attack Argon, and using his Optical Conduction, he deflects one of her lasers and lunges at her, only to get hit with a stun special and lose her in the process. Argon declares that fighting two opponents with anti laser abilities would be too hard and just disappears. Before the battle ends, Crow tells the barely alive Cerberus to meet him the real world at a specific spot.
Back in the real world, Haru and (from a distance) Hime go to meetup spot, but Cerberus, who turns out to be actually male for once, shows himself for only a second before running away.
Hime refuses Haru's proposition to search for irl Karen, but before they can leave she shows herself to them. The two girls have a heartfelt reunion and after they all go back to Haru's place.
Karen, who's real name is Himi Akira, unblocks Haru's memories of her, and tells them that the reason she went to Suginami that day was to warn them that she thinks the ARS is going to try to reproduce the Chrome Disaster armor, using the core of the IS kit to accumulate negative IS energy and use Cerberus as a host (who she said reminded her strongly of Magnesium Drake, her old rival who went on the become the second Chrome Disaster). They discuss for a while about what Enforced Armament could take the place of The Infinity, but don't come to any real conclusion.
Two days later Akira is oficially entered back into Nega Nebula and meets with Raker and Maiden. After their tearful reunion they get ready for the week's area battle. Chiyu and Taku can't participate due to school festival preparations, so Haru get's paired with Karen and Maiden, who nominate him as the leader for the day.
The get into a battle with a Prominence group led by Blaze Heart, who are breaking the Prominence/NN truce by attacking them. When confronted, they claim that Black Lotus had attempted to put a ten men Prominence hunting party including Scarlet Rain under perpetual enemy kill state by riding on a legend level enemy and sicking it on them, and had come to take satisfaction with Lotus without Rain's permission.
The are initially in disavantage do to Crow being to slow to give orders, but eventually Haru has a hot blooded confrontation with Blaze that convices them that they really believe Lotus would never do that. The other two get easily taker care of by Maiden/Karen.
Before the battle ends, they tell them that Lotus ran away by melting into the ground and disappearing.
When Haru gets back home, Niko is waiting for him. She apologizes about the attack and asks him about the fake Lotus, who she claimed had a much weaker "data pressure" than the real Lotus "as if it weren't even really there". Haru promisses to tell her the whole truth about Black Vise and the ARS. But first they go make curry together (turns out Niko is actually terrible at cooking anything other than pastry, but they actually manage to make it passable) eat, do homework together, and get ready to sleep. After Haru is already half-asleep she goes to his room and reminds him that they forgot what they were actually supposed to talk about.
Haru them tells her about about Black Vise. Niko says that the objective of the attack was probably to test her strength, and regrets the fact the she used her new ability at the time and was probably seem.She also mentions that she never heard of two avatars with the same color and that "Black Vise" may be a fake name.
She then confesses had often wondered if there wasn't a way to change your color, so she could be a true "Red" like rider, which she segues into a fit of self loathing where she admits she know she can't beat any of the other kings one-on-one, and is afraid that she might not be able to protect Prominence if the other legions choose to attack them. She says that when she first contacted Haru, aside from the CD thing she was also planning to use Haru as insurance to stop NN from attacking them, all of that while hugging and crying into his chest. After a lot of skinship, Haru swears to protect her at all costs (still hugging). She recovers a bit, and kisses him on the cheek before they fall asleep together in the bed.
The next day they wake up and go together to the school festival. Halfway through they meet up with Pard and the two girls go ahead, promissing to meet up at the gate after Haru is done setting up his class' presentation.
Later at the gate, Haru meets up with the Prominence duo and Rin, who quickly figure out the other is a buster linker. Rin grabs Haru's shirt as usual and Niko mimicks her out of jealousy. Haru notices Rin doesn't look too healthy.
General festival stuff happen, they meet up with Fuuko and Akira, and Haru notices some tension between Akira and Pard. They do more festival stuff, Rin and Pard become quick friends due to their love of bikes, fanservice happens, they go watch Taku's samurai dance thing which is pretty much the only time he gets any attention in the book. Rin then faints, and they carry her to the infirmary.
Rin reveals to Haru and Fuuko that she had been infected with the IS kit. They decide to ask Ash directly about it, and Fuuko has a cabled duel with Rin with Haru as audience.
Turns out the IS kit was implanted in the bike by Magent Scissor. It has changed form to the point of looking like a living creature, with Ash himself incapsulated in some material that fused with the bike. Fuuko dodges the bike's enhanced ramming attack with her soupped-up wheelchair, blocks it's double dark shot with her IS ability Swirl Sway, and then uses the Gale Thruster to destroy the bike from below without killing Ash.
They wake him up, and he explains that because the kit is implanted on the enhanced armament and not on him, Maiden's purification and Bell's time reversal won't suffice to remove it, as it requires a will on the part of the host to discard it (a similar case to Taku's, but he doesn't believe Rin has the mental fortitute to resist the kit long enough for them to do what they did with him). He says that he and Rin had come to the festival prepaired for that to be their last memories as BL, and as NN to enlist him so Lotus can use the Judgement Blow to finish him off.
Haru refuses and instead proposes that they go immediatly to destroy the kit core.
They get ready to go with the prominence duo + NN - Karen, when Pard proposes that they use the 7 in-game days they had to complete the plan to first rescue Karen. Niko claims the reason Pard hasn't been leveling up is specificaly in order to rescure her.
They go to the neutral field, where Niko uses her new ability that turns her enhanced armament Invincible into a mobile armed vehicle.
In the end they are riding towards the palace in the Nikobus in order to face the dragon god Seiryuu.
Additional stuff.
-Karen can put part of her water armor into other water bodies, allowing her to use her ability "water auditory" to scout distant locations.
-Karen can use any water found in the stages to replenish her armor, but she need to purify it first, so the more soiled it is the longer it takes.
-Karen's memory leak and memory free use bb's memory erasing system to manipulate other's memories, but it only works on memories that regard her. She also used it on Cyan Pile at some nonspecified point.
-She calls KYH Sacchi, but it is specifically said by Haru that that is mearly a shortenned for of the nicknames that Fuuko and Utai use (Sacchan and Sacchin), and she doesn't seem to know her real name until they meet in real life.
-Rain can measure other avatars "Data Pressure" due to an IS ability called Vision Extention, and it is something it seems only she can do.
-Prominence is the smallest of the 7 legions after NN, with only 30 odd members.
-Very few of the original Prominece members are still in the new one.Blaze Heart and the other were apparently some of those few.
-Niko implies all of the the other kings can use "power enhancement" IS.
-Karen is almost certainly Pard's parent.
-Two of Haruyuki's classmates get introduced: an boy named Oka and a girl named Ikuzawa, who's the class president.
-Niko says the reason female BL's fawn over him is that they are usually afraid of males due to sensing the diference between their avatars and their helpless real selves, but Haru can make them feel confortable. Haru isn't completely happy of being seen as harmless.
-Blaze Heart, Peach Parasol and Ochre Prision are fan submitted avatars.
oh, also, Karen may have know Falcon and Blossom personally.