A summary of season one of Tensei shitara Slime Datta Ken with some extra content leading into season two.

Ifrit, who has been trapped in Rimuru due to the latter's Predator skill, recaps events of the season while in a discussion with Veldora as they play Shogi.

As far as it goes, many boys, especially in their teenage years, want to have a girlfriend. Keiki Kiryuu is no exception. One eventful afternoon, his days of yearning for a lover seem to come to an end when he receives a love letter from an anonymous sender—along with a pair of white panties. To determine the identity of his secret admirer, referred to as Cinderella, he proceeds to investigate several possible candidates including his senior Sayuki Tokihara, his underclassman Yuika Koga, and his classmate Mao Nanjou. However, as Keiki seeks to uncover who this mystery girl might be, he comes to know about the perverted fetishes hidden behind each candidate's innocent exteriors... [Written by MAL Rewrite]

For the past 13 years, the Nefarious Monster Army have appeared beneath their floating fortress every Sunday to advance their goal of conquering Earth. Luckily, the Dragon Keepers are here to save the day! Having defeated the majority of the monsters during their initial invasion, the heroes now routinely show up to clear away any remnants of resistance. Unbeknownst to the public, however, every fight beyond the first has been a deliberate show put on by both sides: the Dragon Keepers reap the fame and prestige from fighting imaginary enemies, while the surviving weakest monsters, altogether called Dusters, are allowed to live for another day. Sentouin D, a Duster tired of living this life of shame, leaves the fortress in an attempt to overturn his fate. With the unexpected help of the mysterious ranger Yumeko Suzukiri, he discovers the key to defeating the Dragon Keepers lies in their Divine Artifacts—ultimate weapons crucial to the rangers' transformation and unique powers. Teaming up with Suzukiri to infiltrate the garrison of Red Keeper Sousei Akabane, Sentouin D must defy all expectations to save his species from the cruel hands of humans.