Berem was a werewolf Geralt met in 1272 if Ciri didn't come back through the portal in Tor Gvalch'ca. Geralt came to Velen to hunt down the last of the three crone sisters, Weavess, and take back Ciri's stolen witcher medallion, which was originally Vesemir's.
If Geralt kills Berem: Geralt decided Berem was too much a threat and killed him to protect the area, and Geralt found Weavess on his own.
If Geralt allows Berem to live: Geralt saw that Berem could help him, getting the werewolf to take him through the swamp and lead him to Weavess.
- Something Ends, Something Begins (dependent)