A number of proper names in Berserk are written in kanji with furigana attached to show the way they should be pronounced. Typically, furigana is simply used to help people know a "difficult" word's pronunciation, and that's why they're common with shounen manga, since they're aimed at children. In that case, Hiragana is used. Since Berserk is aimed at an adult audience, that's not the case.
Instead, Miura is essentially using the kanji to give additional information on the name. An unfortunate side effect of this is that when translated, the added information is usually lost. One example we've already seen is Idea of Evil, with "idea" being the pronunciation added as furigana to a complex word. Anyway, I figured it'd be interesting to go through some more of these names.
And to begin with, I've chosen Rakshas!
The kanji for his name is 夜魔, which would normally be pronounced YORUMA. 夜 (YORU) means "night" and as for 魔 (MA), well we've seen it a bunch of times. In this context, the meaning would be "demon" rather than "evil", which gives us "Night Demon". This relates to Rakshas' identity as an assassin, a glimpse of which is shown to us in episodes 338 to 341. Regarding the furigana, ラクシャス (RAKUSHASU) is derived from the Indian word Rakshasa. There is however no real connection to the mythological creature.