Out of my depth - how do I deal with the worrying anime and manga content my teen looks at online?? (TW: self harm and sexual violence)

Hi all,

I'm new to the forum (and my eldest has only recently been diagnosed) but felt like this would be a good place to turn for some support.

I'm really shaken after seeing what my 14 year old transgender son has been looking at online. To say I feel out of my depth would be an understatement. My initial reaction was utter revulsion, but I know that any form of confrontation needs to be avoided and  'forbidding' him to look at certain sites will have a very negative impact on our somewhat fragile relationship.

I won't go into too much detail - I have never had to post anything online before that includes a trigger warning, but thought it might be wise to include one here. Just in case.

He's completely obsessed by anime and manga. I've been concerned about the 'dark' themes of the anime series he watches for a while now, lots of psychopaths and death themes etc, but he seems completely oblivious to it all. Often he'll want to show me clips or montages from his current series and sometimes I have to refuse and explain that I find the whole premise of the story deeply upsetting. Most recently he's been reading a manga comic online about an abusive and violent male relationship, so I've spoken to him about it to ask him if he knows that's not what a healthy, loving relationship looks like etc. However, I didn't realise how bad it was until this afternoon. I feel physically sick to look at it. 

Ultimately, I spend every day walking on egg shells with this kid. Self-harm is still an ongoing worry so I'm really stuck on how to navigate this as a parent when the usual 'teenager' approaches are a no-go. There has to be a hard line though, doesn't there? - I mean, it would be irresponsible of me not to prevent him accessing stuff like this, but I know that as soon as I take away access to it, things are going to blow up in a big way. I guess I'm scared of his reaction and the meltdown that will result.

Our situation is probably fairly 'niche', but I'd love to hear from anyone who's had to take a firm line and say NO to something and how they went about it. Obviously our children are all different, but I feel totally overwhelmed and have no clue how to best approach it. 

Thanks for reading x