Short version: The Gintama of harem anime.
Long version: By the time he graduated middle school, Rentaro Aijo has confessed to girls he loved 100 times and each and every time he was rejected. Praying to the gods at a temple, he's told that but only will be blessed to meet his destined soulmate in high school, but he will have one hundred of them. He runs into the first two immediately, but soon after learns that if he chooses one, the other will die.
Rentaro's solution: openly date them both and invite any later soulmates into the harem. As of this writing he's at 26 girlfriends and counting.
The anime started this weekend and is currently streaming on Crunchyroll: https://www.crunchyroll.com/series/GNVHKN933
As noted by the post below, the "or they'll die" thing is basically just an excuse to not pick one girl and never really comes up again. The series is all about the hilarious antics Rentaro's Family get up to as the girls are quite the quirky bunch, and Rentaro himself isn't any better.
A playlist of the trailers two for the anime in general and one each for the first five girlfriends.
The anime opening:
The anime ending:
Finally, a Youtube video quickly describing each girlfriend up to #22: