Here's my attempt. I removed some of your AA that I felt was making the image too blurry, and I AAed all the thin lines. I think there are still some places where the AA (mine included) might be too soft, but hopefully this'll give you some ideas on how to AA thin lines in your future work. In some places, to maintain the look of thin lines, I had to not use the dark line colour at all. The biggest section of this is near the top of his head.
I also changed the AA colour on the red bits because it was so similar to one of the tan colours. You don't have to copy this change, I just wanted to demonstrate that for AA, the hue usually doesn't matter as much as the value (how dark/light it is) does.
While AAing, I noticed you seemed to create a lot of the lines out of straight line segments. That's not an issue in itself, but you have some noticeable corners where the differently angled lines meet. I did not change these, but I think a bit of extra care in those areas would help. With AA, you can make otherwise "jagged" lines look smooth, which can help a lot with creating gentle curves.
Something else to think about is whether you want such thin lines everywhere to begin with. The TG manga has some nice line weight variation, there are both thick and thin lines, which help create volume and make the art look more dynamic. Pixel art of this scale is much more like a drawing, so drawing techniques line line width variation apply in addition to pixel-level techniques.
If you'd like, you can go ahead! =]
Thank you for the feedback, I'll try to AA the thin lines, too.
To AA thin lines, your AA colours will often need to replace the dark colour of the line, like here. AAing thin lines is quite difficult because of the thickness issue, but it is doable and this looks like a great piece to practice that.
You could also reduce the AA on the AAed parts, similar to what SpaceSalcom said. I don't think eliminating it entirely would look that good, but making it simpler and using it only where it's really, really needed might help it not stand out as much from the un-AAed lines. Either could look good, but I feel like extra practice with AA never hurts. I'm even temtped to give it a shot myself, if you don't mind!
Whichever option you pick, if you decide to continue work on this, I think you should remove some of your existing AA, especially on the 45 degree lines. That AA just makes the image look blurry. 45 degree lines don't usually need AA, just as horizontal and vertical lines don't.
You could just have done it with 2 colors and it would look better. The AA contributes nothing tbh.
I tried to AA the thin lines but it kept becoming thick or didn't look good. I don't know how to AA the thin lines.
It feels unfinished, with so much of it AAed and some of it not AAed. I think AAing the thin outlines would really help pull it together.
A huge thank you! =D I'll keep the AA technique and style [that depends on the art size] in mind.