Muramana on Ryze? (Viable in D5 if played right)

I was on the Twitch mains subreddit when I saw this support main looking for a Diamond Twitch main. Interested to see what champions he played (ugh - Janna main) I clicked onto his profile and scrolled down to see a Ryze game that was played a few days ago and was confused because I saw Muramana in his item build (and a tear). Seeing as he plays in Diamond and is able to play viably with this build, could someone tell me how this works? Or how it'd be better than Seraphs embrace? (He opts to build it over Seraphs if he needs other situational items)

Tl; dr - Muramana on Ryze in D5 - Viable? Also How does it work? Why does he opt to build it over Seraphs?