I know what alignment is and how it works on the planes. I feel like I have a partial answer in there but I need some clarification.
Ok, so just to clarify, are you guys saying you want just the main character to have an alignment that is affected by their actions?
Yes
Would people react to it?
Yes
Who would see alignment?
Just you? I think, I am not clear on this, but other people would be aware of your reputation.
So would you be able to see anyone else's alignment? Companions for example?
And for me this is the sticking point. I don't think you should be able to know your companions Alignment, because why would you?
And forgive me, but I don't need a dissertation on alignment. My biggest complaint about alignment is that its been WAY overused in the past. Larian has it right by limiting the use of alignment because it ruins narrative structure.
The way BG1 and BG2 did alignment was absolutely silly. Everybody's alignment right there to be seen.
Respectfully, I feel like I answered all of your questions in your last response. But to answer your new questions, no, everyone can have an alignment. No, people wouldn't react to a character's alignment unless they're capable of doing so. Each player/character can directly view their own alignment, as well as the DM, the game itself and any other entities which should have the ability to do so.
