WARNING: The following contains spoilers for Episode 9 of I've Been Killing Slimes for 300 Years and Maxed Out My Level, now streaming on Crunchyroll.
Azusa Aizawa, the witch of the highlands, spent an incredible 300 years killing low-level slimes to grind money and experience points. After three centuries, those slime spirits coalesced into two girls, Falfa and Shalsha, who were determined to meet their "mother." They soon formed a happy foster family in Azusa's cottage, but now there's trouble.
Shalsha, the younger sister, cries out to Azusa that Falfa has woken up in the body of a true slime and lost her human form entirely. Azusa is ready to search high and low to find a solution. She isn't a fighter in this isekai world, rather a healer and nurturer, but she'll do anything for her foster daughters. Even summon demons.
Azusa Hunts For Answers to Help Falfa
Halkara, Laika and the others can hardly believe their eyes when they see Falfa in her unassuming slime body, and it's pointed out that a demon would probably know what to do. So Azusa summons her old friend Beelzebub, who, after climbing out of the bath (yet again), brings a small party to the demon capital to consult the Intelligent Slime. The demon king points the way, and Intelligent Slime urges Azusa to visit another faraway realm: the Tomuriana province's tallest mountain, where they'll meet Magician Slime. Azusa's party visits the next day, and Magician Slime, who has a humanoid body, urges them to visit the southern town of Kelney -- where Fighter Slime is visiting.
This is the solution they needed. Magician Slime determined that Falfa's problem is physical, since the poor girl slept oddly and mutated into a slime form. Fighter Slime assumes a human body through physical conditioning alone, so Azusa and the crew visit Kelney and enter the martial arts tournament there to impress the one who often calls herself "Fightie." Azusa will go anywhere and do anything to help her friends in I've Been Killing Slimes, and entering a competitive tournament like this is a small price to pay.
Azusa Makes Another Slime Friend: Fightie
Azusa and Beelzebub both enter the tournament to get a chance to meet Fightie, but it's the latter who's successful first, knocking Fightie out during their semi-final match. So the final is Azusa vs Beelzebub as a grudge match, and Azusa cleans house. Beelzebub admits defeat, but more importantly, they get a proper chance to meet Fightie -- who wants to test her mettle against Azusa in an informal match. However, she faints from terror upon sensing Azusa's slime-killing aura.
All is well when Fightie wakes up, and she is deeply impressed with both Azusa and Beelzebub. She's eager to have one or both of them as a martial arts tutor, and best of all, Fightie finds a way to get Falfa back to normal. Azusa is immensely relieved and embraces both daughters, then does Fightie a favor and sets her up with Beelzebub as a teacher. Azusa barely even knows this martial artist slime, but if she can adopt the sisters Falfa and Shalsha, she can do a favor for Fightie too. Despite the source of her strength, Azusa is becoming I've Been Killing Slimes' #1 slime mother.