I'm thinking in starting Demon's Souls again with a new character but I also want to know if I delete the only character I have now in my save file will cause to lose my trophies.
Trophies work at a system level. They don't care about your save files at all.
And actually, there is no way to lose trophies. Not even if you wanted
to. Assuming that they have been synced, anyway. Every embarrassing game you have ever played will be on record forever!
When PSN went down this year my PS3 was a mess so I just reset the console and did a new account on PSN when all of that ended, I also sold some of my games that I knew will never touch again (I still have like 5 games to sell actually).
Anyways, thanks for the reply.