Konosuba Light Novel Volume 12/Synopsis

Chapter 1
The girl teased in Volume 11 who called Darkness "mommy", Sylphina, turns out to be a Dustiness child that Darkness babysat. Due to unfortunate genetics, she was born prone to sickness. Hearing the news, Aqua slips away to spread it around the city. Megumin, Kazuma and Sylphina then play a game together as Darkness runs off to chase Aqua. That night, while Kazuma sat in his bedroom playing a video game console, Megumin sneaks into his room and discuss their relationship. After numerous heated romantic arguments, Kazuma expresses romantic interest in Megumin and a desire to procreate. Megumin is taken aback; eventually, they arrive at the conclusion to start dating but keep it secret from the rest of their party.

Chapter 2
Kazuma and Megumin wake up early in preparation for their first date. Under the guise of a regular explosion walk, they bring Aqua along to make sure nothing goes overboard. Aqua discovers that explosions make good fish traps. As they return, they find many adventurers lined up at the guild. Luna then announces that the guild will collect taxes in response to the recent spree of mission completion to combat laziness. Those who manage to avoid being caught will be exempt. Darkness surprises Kazuma by chaining herself to him after loading herself with lead blocks and hiding the key in the yard. Megumin ends up exempt due to her low income status. Aqua ends up escaping after casting strength buffs on Kazuma by hiding inside a small water reservoir, Kazuma himself escaping by assaulting a police officer and hiding in jail. It is lastly revealed that Darkness had initiated the tax collection.

Chapter 3
By the time the party returns, it was already dark. Darkness could not find the key. After dinner, Kazuma insists that he take a bath. He end up tearing his shirt off and bathing as Darkness sat outside of the tub. After the bath, Kazuma and Darkness must sleep together. Kazuma wakes up midnight to find Darkness drooling on him, alerting him. When they try to go back to sleep, Darkness confronts Kazuma about his relationship with Megumin. Darkness starts by explaining her odd preference in males and how it has changed over time then eventually confessing to Kazuma that she also loves him. Afterwards, she has a semi-breakdown when she was formally rejected by Kazuma and expresses her wish that the party dynamic remain the way it is forever. As she recollects herself, she decides to leave Kazuma's romance circle and his bedroom but forgets that she was still chained to him, resulting in a humiliating exit. After this, she has a major breakdown before kissing Kazuma on the lips. She then tries to rape him but with little success as she has no idea how to rape. With comedic timing, Aqua and Megumin arrive after finding the key to the handcuffs just as Darkness is about to attempt something lewd.

Chapter 4
Kazuma and some adventurers at the guild question what Darkness is doing with her tax money. They then go investigate to find out that she has been running an orphanage, and the new funds had been used on school supplies and healthcare for the children. The reason for the tax collection was because the orphanage had recently suffered a failure in transaction from its proper source of funding. As Darkness explained the above, Kazuma and company immediately feel guilty and ashamed for doubting Darkness. Darkness then return to find the children all sick and unconscious. Sylphina was found to have spread a severe disease to other children, and the cure requires the fingernail of a powerful demon as an ingredient. Vanir explains that he knows of a friend who lives in solitude under the guise of Duke Saierhilde.

Chapter 5
Kazuma and Darkness go hunt for Vanir's friend as Aqua heals the children and Megumin prepares the concoction. They spend another night together in a wild cave, but it was cut short when Darkness uses Wiz's noise-making portable toilet. They proceed to ride through the night and arrive at Duke Saierhilde's castle. The demon turns out to wear a penguin hoodie and has a hobby in collecting rare monsters and watching them fight. He offers to give them his fingernail if they pass his monster fighting challenge. Darkness enters his underground colosseum and faces against two waves of monsters. The first wave consisted of a bunch of goblins, who Darkness cannot hit at all; Saierhilde thought that Darkness was showing off her endurance and pitying the goblins, so he tells them to retreat. The second wave consisted of a few rare specimens of male orcs, who are naturally afraid of females and refuse to fight. Seeing his monsters fail, Saierhilde jumps out of his suit and fights Darkness himself, defeating her.

Chapter 6
Failing to obtain the fingernail, Kazuma and Darkness go to sleep at a local hotel when they meet Chris, who had followed along since Darkness prayed to Eris before the trip. Chris then excitedly offers to help them infiltrate the castle and forcibly obtain whatever they were after. On the way, Chris asks Kazuma about his relationship with Darkness, to which he responds that it is complicated as he has kissed Darkness even though he's technically in a relationship with Megumin. Chris decides to not pry further. Taking Darkness as an additional member of the Silver Hair Thieving Group, they sneak into the castle. Chris then unfortunately bumps into the male orcs patrolling the arena, who then mistake her for being male and try to strip her. Darkness follows up and dispels the orcs. After reaching the demon himself, Chris realizes what Kazuma and Darkness had been after and aggressively attacks him. With Darkness holding the demon down, Chris manages to cut off a hand. She later descends as Goddess Eris after Darkness fell unconscious to punish the demon, forcing him back into hell. On their way back, Chris expresses interest to Kazuma to eventually reveal her true identity to Darkness, who overhears the statement. With the final ingredient in place, they finish creating the medicine and cure the children.

Epilogue
The whole party goes on an explosion walk with Megumin. After the explosion, Aqua goes again to catch the fish killed by the explosion while Darkness sexually harasses the helpless Megumin. Later, Kazuma rests on the side as the rest of the party cook fish. Darkness then approaches him and tells him that she accepts Kazuma's relationship with Megumin; however, she also states that she still hopes Kazuma will allow her to occasionally harass him sexually before kissing him a second time. Kazuma is shocked as Aqua runs to the guild to spread the news about Darkness' new development. In the frenzy, Kazuma wishes that the party dynamic remain the way it is forever.