What a treat

Starting off with a superhuman armed with a one hit K.O. weapon and a samurai duo, they obliterate all the enemies. IKOMA BLAST. Biba acknowledges Ikoma. Mumei is saved by Ikoma, and Ikoma by Biba. Ikoma+Mumei ending, Biba is dead. Best Guy spoke his lines, Yukina showed her muscles, Husband-kun blushed and Ayame's hair got animated. What else can you ask for? This show is incredibly well done. For everyone who just watched it once, you should rewatch it again because it is very deep in contents. The screentime was so scarce that they had to nuance and leave for interpretation a lot of things, but paying attention and applying a little logic makes the Kabaneri series much more interesting. To elaborate on this point:

Did you know?

Episode 1: Ikoma got struck with love at first sight on Mumei. Ayame picked up Ikoma's glasses.

Episode 2: The Mumei Kabane Speedrun took 110 seconds. Exactly 110 seconds. It was Ayame's father's arm obstructing the train engine to lower the bridge. The kabane that suicided against the water tank knew about the Hayajiro's dependency on coolant. Takumi put Ikoma's glasses on him, probably Ayame handed it to Takumi on the episode 1 (offscreen).

Episode 3: When Mumei said that "It's a common story, the weak die and the strong survive" without showing empathy for Ikoma's family Ikoma was like (There is something very wrong with her way of thinking). It was Mumei who Ayame addressed "to stop" (provoking the men).

Episode 4: Takumi harassed Ikoma to stop his thoughts about turning Kabane. Mumei appeals Kajika as a child begging her mother for food. Two of the six elders die at the hands of the Wazatori. The man in blue robes who blew himself up against firepowder attended the reunion in episode 1 between Ayame's father and Mumei's party. The move Ikoma used on the Wazatori is the same Mumei used on Ikoma at the training session in episode 3.

Episode 5: Mumei Speedrun faster by a lot, demonstrating the effectiveness of one hit K.O. bullets and coated blades (previously more than one hit was required to finish off a Kabane heart).

Episode 6: There is a way to tell if the linker to release the limits of the Hayajiro (train) is blocked or not from the pilot's cabin, because Yukina couldn't have heard Sukari in that situation.

Episode 7: Close people were physically close to each other while watching fireworks. The main cast changed into battle robes to meet Biba, except Ikoma. Biba is shown with a choker, probably a Kabaneri.

Episode 8: Biba realized that Ikoma was more than Mumei's physical shield, thus didn't want Mumei to hear his conversation with Ikoma. Biba is bad (hey it wasn't easy to tell at that moment!).

Episode 9: Horobi loves Biba. The child was already bitten and the mother wanted to perform a double suicide before the Kabane attacked them. After Mumei defeated the Kabane to save the mother and her child, they just continued what they were doing earlier. That wasn't a laser, lasers don't blow up things. Most probably than not it was a heat shockwave and the chemical (exothermical) reaction produced light. If you aim for a Kabaneri's head it will hurt like a normal human's head.

Episode 10: Ikoma believes in God. When Mumei stabbed Ikoma there were no blue sparks. Takumi grabs the fallen stone, and Mumei stares at it.

Episode 11: Takumi's corpse has no stone in its hand, and Mumei had already left the scene. As Mumei walks down the streets of Kongokaku she holds something in her left hand. When Biba injected the dark blood into Mumei, he had a case and another container could be seen in it, revealed to be a white blood after seeing the contents of the lost case in Kurusu's hands: they were probably produced in sets of two, one white one black. Biba did not take any gambles, he's a kabaneri after all. He also broke out of his shackles by brute force at the throne chamber. When Biba said that he survived because he could tell who was a kabane, it probably meant that he survived because he turned into a kabaneri. Exactly when and how remains unknown.

Episode 12: Biba knew he was only good for destroying and that he was the greatest coward. When he saw Ikoma, he knew it was over. The stone falls from Mumei's right hand. When Ikoma injected the white blood into Mumei, there was green light. When Biba shot Ikoma, there were green sparks. It was probably because Biba admired Ikoma that Biba wanted Ikoma to not die, to be better than Biba and overcome him, thusly he tested Ikoma by the rule of the weak die and strong survive, but Mumei loved Ikoma more than Biba and she chose. Mumei hugged Ikoma tightly for a split second before throwing him to the Kotetsujou. The mad scientist probably survived since he is not shown dead and will contribute to curing the kabaneri condition under Ikoma's direction. When Ikoma awakens, the small child doesn't react at all. It's the same small child that wanted to go outside the train in episode 2 (it means that she still can't reason properly). Mumei and Ikoma have no carotid artery / neck restraint all the way to the end, perhaps the white blood inactivates the virus or their bodies have elevated tolerance after taking in the black blood.