It is the time of year when the people of Axel host an festival in honour of the Goddess Eris, to thank her for her blessing in allowing them to survive for another year. When Aqua heard of this, she complained loudly to Kazuma, wondering why there was no festival for herself, as she is Eris's senpai, and wanted to replace the Eris festival with an Aqua festival.
Kazuma, who has learned the cooking skill since the rescue of Darkness, initially did not want to participate in this event, since he is now the wealthiest adventurer in Axel and did not want to get involved in anything troublesome, instead wanting to just open a restaurant and live peacefully, however, Aqua roped in Megumin and Chris (Eris) into her plan.
Chris on the other hand, spoke to Kazuma and Darkness about the divine relics and that one of her goals was to find them and seal them. She also managed to find another Divine Relic in Axel, in another noble's home - The Divine Armour Ignis. Her plan was to use the festivities of the upcoming festival as a cover to infiltrate the mansion and steal the relic.
Aqua went to the recently established Aqua church in Axel to gather her followers to host an Aqua festival. Megumin was previously in the care of the Aqua cult, and met her acquaintance, Cecily, a priestess of the Axis Cult, who has an obsession with Tokoroten Slime (Chewing Gum). After Aqua declared that she wanted to host a festival, the Axis members were all for it, and Kazuma was unwittingly roped into helping them. While negotiating with the festival committee, Kazuma convinced them to hold 2 festivals simultaneously, and pit them against each other to increase profits. For this, he was made festival advisor, and would receive a cut of the profits.
Later that night, Chris and Kazuma attempted to steal the divine relic, but were busted when they found out that Aegis) was able to talk, and that he refused to be stolen unless his new master was to be a cute swordswoman. When Eris and Kazuma tried to take him, he screamed and awakened the guards in the mansion, so they had to retreat.
The next day, Kazuma, Aqua, Darkness and Megumin participated in a monster hunting quest with other parties of adventurers, to prepare for the festivals, and Aqua impressed Kazuma. Of course, during the fight that followed, Megumin could not control her love of explosions and fired a shot, levelling up and attracting all the monsters in the forest, while Darkness purposely put on too much monster attraction solution to get more monsters to hit her, eventually even attracting ants, who found their way into her armour.
After returning safely, Kazuma went over to the festival committee to advise, suggesting that the women put on swimsuits, play with water, and even managed a cosplay theme, and also managed to get the succubus onee-sans to participate in their true forms.
The Next day, the festivities started, and it turned out the Axis cult ran stalls that cheated people of their money and setting up stalls that were scams or sacrilegious (shooting stall with the Goddess Eris as the target), and there was one lottery shop in the Axis cult that was run by Chris, who as the goddess of luck, didn't allow any one to win, therefore losing customer support, so Aqua asked Kazuma to help her, which he did by cooking yakisoba, as the Axis cult losing money would mean less profits for him, and he could foresee Aqua asking him for money to cover their debts if they did, and managed to also give them some ideas to make a profit. He then wanted to resign as the advisor as he found out that Aqua just sincerely wante to enjoy the festivities and used her money from defeating the Hydra and other savings she set aside for Emperor Zell to fund the Axis cult and to rebuild their diapilated church in Axel. However, that night, as thanks for allowing the succubi to participate in the events he was served drinks by 2 of them, including a Lolita succubus that was featured in the anime and was convinced to stay on as an advisor.
The third day saw Megumin inviting him to the fireworks festival, raising his expectations, only to have her taken away by Yun Yun who was firing fireballs into the night sky to create said fireworks. When Megumin wanted to fire an explosion into the sky to join in, she was arrested and thrown into jail. Darkness also approached him and created a good mood, thanking him for saving her, and kissed him on the cheek for his reward for slaying the Hydra (Vol. 7). Feeling disappointed with just a kiss when the mood was so erotic, he gets approached by Chris for another attempt to steal Ignis, and they infiltrate the mansion again. This time, seeing how Ignis is able to speak, Kazuma brought a noise nullifier so Ignis could not wake the guards. When Ignis realised that, he broke off the chains holding him and ran away from the House to look for a pretty woman worthy of wearing him, and sent a telepathic message to the members of the noble house, waking them and the guards up, forcing Kazuma and Eris to run away.
After escaping, Darkness tracked down Kazuma and Chris to punish them for the disturbance, but later let them go when Kazuma started spilling out secrets between himself and Darkness in front of Chris. They hatched a plan to capture Ignis by planning to hold a beauty contest, and were preparing to lie in wait for him, but he unexpectedly showed up when the first contestant entered, leading Kazuma to capture him using a net, but, as each contestant entered the stage, they kept getting distracted and calling for truces to admire the contestants beauty. When Darkness, who was convinced by Kazuma to participate, went on stage, Ignis was amazed by her beauty and wanted her to be his master, but, caught up in the mood, Kazuma and the other adventurers taunted Darkness who went berserk and attacked them ruining the festival. Chris appeared at that moment, having gone away to buy drinks, and spoke once more to Ignis, revealing her identity and promising to find him a good master, but Ignis, unconvinced on both points, gets Eris angry but right at that moment, Kazuma intervenes and requests something of Chris. Chris then participates in the Beauty contest as Eris herself, calming the crowds down with her beauty and cuteness, and Ignis is both amazed and finally believes that Chris is Eris. The crowd then goes wild as their object of their worship is there in physical form, and mob her to get her blessing. Panicked, Kazuma asks Ignis to save Eris, which he did, and to take her away safely while Kazuma himself provides the distraction for them to get away.
Continuing from the end of Volume 7, Chris is revealed to be the form that Eris adopts in the mortal world when she is not doing her duties in Heaven.
As Alderp's misdeeds were found out, and Kazuma received the money he lost in Vol. 7 as a special exception, and the Dustiness family is now the reigning governors of Axel.
Darkness found out about Kazuma's role as the festival advisor and the money he is to receive, and gets informed of Aqua and her follower's multi-level marketing scam, who he had unwittingly told her about. Out of guilt, he donates the money he was to make as an advisor to the Axis cult. In the post festival party, the Eris and Axis cult is shown getting along together and that the Eris and Aqua festival would carry on next year. Axel also gained a reputation as the town where the Goddess(es) descended, and this boosted Axel's economy. As Kazuma and Eris took a break from the party, Kazuma told Eris saying that she is the only one that he respects as she has been working so hard behind the scenes all the time, and teased her by asking her to marry him, to which she responded by blushing furiously and being embarrassed.
When reaching home, he receives a letter from the Axis Church in Axel, informing him that he has been made an honorary member of the Axis cult for his large donation and help in the festival, to which is reaction is to tear up the letter and scream, while Darkness informs them that her duties as the temporary lord is over as her father has healed enough to resume his duties.
The volume ends with Megumin inviting Kazuma to her room that night as she wants to give him something as a birthday present as that she has something important to say to him.