It's been a few years since I saw Busou Renkin, so I don't know if my two cents are reliable enough for you, but I wouldn't recommend watching it - less because of content, more because it just isn't worth it. After a very interesting and promising beginning, I found that Busou Renkin devolved into annoying shounen tropes and just...utter ridiculousness. Sorry, no, I can't take an anime seriously if the villains are named things like Moonface (who has a waxing/waning moon for a face) and Dr. Butterfly (whose moustache is shaped like a butterfly) *facepalm* The ending is also one of the most boring, anticlimactic endings to any anime I've ever seen.
As for content, most of what I remember is pretty average for anime - maybe some crude jokes or a bit of innuendo. The two things that I really found objectionable were a brother-sister duo who have a really
disturbing couple of episodes where they say the words to a traditional wedding vow to each other :/ That really creeped me out and almost made me stop watching. The other really disturbing thing is one of the main villains, Papillon. He wears a skintight leotard and/or a pink speedo...that he rummages around in, because apparently that's a great place to store his belongings?!
I wouldn't bother with Busou Renkin if I were you. Don't waste your time - go find something more worthwhile.
You can find out things about the past that you never knew. And from what you've learned, you may see some things differently in the present. You're the one that changes. Not the past.
- Ellone, Final Fantasy VIII
"There's a difference between maliciously offending somebody - on purpose - and somebody being offended by...truth. If you're offended by the truth,
that's your problem. I have no obligation to not offend you if I'm speaking the truth. The truth is supposed
to offend you; that's how you know you don't got it."
- Brad Stine