What's the anime about a redhead whose friend uses magic? I was watching an anime and closed out of it, and now can't get back to it.

Description of the anime: A redhead male lead whose friend learns magic to find the killer of his sister, who was secretly the girlfriend of the redhead male lead. 

I was only 3 episodes in on Crunchyroll, so I can't describe it any more. Does anyone know the name of this anime?
The anime you're talking about is Zetsuen no Tempest (or Blast of Tempest, as Crunchyroll translates it). 

It begins with TAKIGAWA Yoshino meeting his long-time friend FUWA Mahiro, who has gained magic powers from KUSARIBE Hakaze (a magician stranded on an island in the middle of nowhere) as part of a deal in which Hakaze will help Mahiro figure out who killed his sister, FUWA Aika. Unbeknownst to Mahiro, Yoshino and Aika were lovers. Drama unfolds thereafter.