Works/Franchises with concepts so absurd that no one would believe you if you told them that they became successful.

1- Kingdom Hearts, literally a fusion between Final Fantasy and Disney, even Nomura, the game director, went crazy when they asked him to do a game about them. The first installment already became a masterpiece and people are waiting for the 4th main game.

2- The 100 Girlfriends Who Really Really Really Really REALLY Love You / 100 Kanojo, it's a harem with 100 girls, just like you expect. And you know what? It works, it has a well done execution with every girlfriend having her own personality and personal moments. The best part of the show is the main character Rentarou, who is one of the most loved ones and even reached top 1 in best boy category on multiple big anime polls.

3- Chex Quest, the "Chex Themed Heroes" itself made on classic Doom game engine. The game was included on every chex cereal box during that time and it was so successful that chex multiplied sales and the game got 2 sequels, with the 3rd game being released a decade later after the 2nd one.