I don't exactly know how popular this thread will be given the nature of this series being a Light Novel. It gotten an anime that has only 2 Seasons (for the moment) and a slow moving manga that will probably still be going on even after the novels end their run. But I'm like, hey this is a fun series for those that know about it or want to find something new to follow.
So let me give you a brief (trust me, it probably won't be brief) rundown of the characters and the setting, while trying to avoid any big time spoilers.
Kazuma Satou~ Just your average 16 year old Neet "Not in Education, Employment, or Training" who enjoys video games and avoiding society. After having promised his childhood friend that he would one day marry her when they we're older, Kazuma saw her ride off with a upper classman. It was at that moment Kazuma decided he would ditch class and spend the rest of his life playing games... That is until his life tragically comes to an end when he leaves his house to pick up a Day 1 exclusive game and attempts to save what he assume to be a girl about to be runover by a truck (I'm promise you, this isn't a drama). It from here on out the real adventure being as Kazuma is reincarnated in another world, with RPG like qualities, in order to defeat the Demon King that terrorizes it. Due to his rather uninspiring lifestyle, his stats are rather average except for his intelligence, which is above average, and his best stat being Luck. Because of this, he's the lowest ranked class of Adventurer, which is a jack of all trades, master of none.
Aqua~ When Kazuma dies, he greeted by the goddess Aqua, seer of the afterlife of Japan. It's here that Aqua grants Kazuma the choice to reincarnate on Earth with no memories of his past life or defeat the Demon King in another world and be granted 1 wish. She offers Kazuma the option of taking 1 item with him that will grant him a rather OP power or ability to give him a chance in the new world. While Aqua might be a goddess, she's rather self absorbed and pretty clueless of many situations. And thanks to her demeanor, the thing Kazuma ultimately chose to take with him to the new world is the goddess herself out of spite for looking down on him. Aqua is an Arc Priest that specializes in stat boost, healing, reincarnating, killing the undead, and her main special ability, PARTY TRICKS!!!
Megumin~ This 12 year old member of the Crimson Demon clan can be summarized in one word: EXPLOSION! Being a Arc Wizard, you'd think that would be a blessing for any party right? Well Explosion is her only spell, a high level attack that completely drains her MP after a single use. Oh, and she's a Chuunibyou.
Darkness~ A Paladin class warrior, this girl is something else entirely. Having devoted her entire being to relying on defense, she has absolutely no offensive capabilities... like seriously, she never hits her target no matter how close they are. She's 18 years old and her personality is rather all over the place. One minute she's the calm collective type, the next she's fawning over the enemy having their way with her. Yes, she's a masochist...
So yeah, it's pretty hilarious to think I can talk so little about the girls and more about Kazuma, but that's story of their adventures in a nutshell. Of coarse we'd know a ton about Kazuma from the get go and it's also why I'm not spoiling at least Megumin's and Darkness's back stories yet until I realize I'm the only guy likely to use this thread at all to say anything. We don't learn a great deal about them till about the early-midway through part of this not quiet complete tale.
Oh yeah, this was actually a web-series before becoming an official Light Novel, but the author himself said he was likely to make some changes, which he has. One of them being the protagonists were all older in the web-series (Kazuma was 20, Aqua still ageless, Megumin was 17 and Darkness was 22)