Neighbors’ war - harassment vs light

I've been living in my current apartment for about a year and a half. It's a privately-owned building, not a mansion/apartment complex, as are the other buildings on the street. Both buildings on either side of me are super close - I'd say about 3 feet at most between buildings.

Recently, I got a new neighbor in one of the buildings next to me, and he has taken to harassing me by banging on my window with a broom any time he knows I'm home, both night and day. He came to my door once to yell at me, but my Japanese isn't great and I didn't really understand what he was saying. After weeks of him yelling and banging on my window, I think I've figured out that the light from my window is shining into his room and bothers him, so he's demanding that I get a heavy curtain to block the light.

Why does he not just get his own curtain? Who knows. Why does he not lower the blinds that are already installed on his window? Who knows.

I don't want to put up a curtain (the window is frosted, so I'm not worried about privacy), because the window has a ledge on which I've decorated with photo-frames and knick-knacks and put other things on. I don't want to have to pay the money for a curtain that I haven't needed for all the time I've been here. And, quite frankly, I just find it stupid that he thinks it's better to actually, actively harass me instead of just buying his own curtain, so there's a principle-of-the-matter element to it.

What would be the best course of action in this situation?
I've considered calling the police and filing a complaint, but I'm worried that the neighbor will file a counter-complaint because of my light, and I feel I'm in a more precarious position than him, since I'm a foreigner. Could calling the police end up hurting me in any way?
Or should I just deal with it and hope he gets bored and stops on his own?

Thank you for any input you may have.

Here are your options:

1. Discuss with your fellow neighbors and see what they have to say.
2. Bring the matter to your "chounaikai" (neighborhood board). Typically, there is a "hancho" of your district. A neighbor would know who the hancho is, if you don't. Or if you're not the owner, your landlord would know.
3. You are always free to discuss it with either your local police station or the koban of your district. Don't call 110 right away unless it's an emergency.
4. You are always free to discuss it with your local city hall, which also often provides free interpreting service. The City hall is there for its "citizens". Even if they can't help you, they could guide you to a place that would.

My personal opinion? You were there first, so you get the priority. But let's hope there is a way to calm your annoying neighbor down before he is forced to move out.