WARNING: the following contains spoilers for Episode 4 of I've Been Killing Slimes For 300 Years and Maxed Out My Level, now streaming on Crunchyroll.
After three centuries of slaughtering slimes to rack up gold and XP, the witch of the highlands, Azusa Aizawa, has made a few new friends, including Laika the red dragon. Unlike the homebody Azusa, who's taking it easy in seclusion, the hardworking Laika has a whole network of friends and family among her kind, and in Episode 4, it's time for Azusa to meet them.
Laika's older sister Leila is about to get married, and Laika invites Azusa, Halkara and the others to watch the nuptials unfold. Laika assumes her dragon form and flies her friends to Mount Rokko, home of the red dragons, only for an ancient feud to rear its ugly head.
At first, all seems well on Mount Rokko, as a couple dozen red dragons gather and chat around giant plates of food. Laika introduces Azusa, Halkara the elf and the rest to her family, including her sister, the bride herself: Leila. But, just as everyone is getting to know each other, trouble strikes. The sisters Falfa and Shalsha and even Halkara cower in terror as a pack of blue dragons show up, led by Flatorte, who has a serious grudge against Laika and Leila. The blue dragons attack with their ice breath, stopping the wedding cold in more than one regard.
Laika and the red dragons fight back, but Flatorte boasts that she's got another pack of dragons attacking Mount Rokko and its town, making it seem as if the blue dragons have already won. But then Azusa leaps into action and takes them on, beating the dragons down with high-powered kicks. The last few blue dragons flee to the hot springs town inside Mount Rokko, and by the time Azusa and the others catch up, they realize that another friendly face has come to help: Beelzebub, Lord of the Flies.
Beelzebub, who's a big fan of Halkara's energy drink Nutri-Spirit, had been taking it easy until Flatorte and her blue dragon cronies showed up in Mount Rokko. Beelzebub, annoyed that her hot springs trip got interrupted, trapped all the blue dragons in arcane runes, giving Azusa a chance to talk things out with the scaly troublemakers. Flatorte is simply jealous that Leila was able to get married while she drives people away with her bad attitude. On request, Flatorte assumes her human form, and she reluctantly agrees to a peace treaty with Laika, who stands for all red dragons. Flatorte is also saddled with the bill for all the property damage from her attack.
With everyone getting along, the wedding resumes and all the dragons assume their human forms for the reception. Leila, the bride, is pleasantly surprised when Flatorte approaches her and offers a red rose, a kind gesture after all the trouble she's caused. Azusa, meanwhile, is simply drinking in all the astonishing sights and sounds of dragon society, having never seen anything like it in this isekai world. Laika, meanwhile, has mixed feelings about all this, since her sister will no longer be around to comfort her when she's feeling down, so Azusa offers to be Laika's new emotional bedrock. Laika is deeply grateful, and all the friends gather at the Mount Rokko hot springs to wrap up the evening in style. Azusa is finally spreading her wings to explore her new world.