ð

The letter ð has a "th" sound to it's technically correct to say Roh-der, but it's more accurate to say Roh-ther (they are not the same xD)

I pronounce it with a "th" sound.

So Rauðrowl would be "roh-ther-owl"

I've been transcribing it using the sound it represents in IPA, which in English we write using "th". However, the katakana suggests that perhaps it's supposed to be something close to a schwa

I've been pronouncing the word "rauðrblade" as "raw-ther-blade"

Or like the word "rather" in a proper British dialect.