Spending my birthday alone in Tokyo after a sad breakup. Ideas for a nice day by myself?

We were in a relationship for several years and things didn't go the way we'd planned. I'm heartbroken. I'm visiting Japan for the first time and I hope traveling will help me find some peace for a couple weeks.

I want to try to have a good birthday in Tokyo next weekend even though I won't have anybody else to celebrate with. I'll be staying at a hotel in Chiyoda.

Is it too late to book myself a relaxing massage or a dinner at a nice restaurant in Tokyo? I don't think I can afford a Michelin restaurant, but eating somewhere above average would be great.

Also, are there other places to visit on my birthday that might be comforting or distracting? Maybe something related to the observance of Obon (お盆)? I don't mind taking a train a little bit outside Tokyo too.

Thank you.

ありがとうございます