Unique places in Tokyo for Non-first timers?

Hello everyone!

My brother and I are visiting Tokyo on March for 6 days.
It's my 3rd time visiting Japan, including the time I studied in Tokyo for a whole year, while it's my brother's first time.

I'm trying to finalize our itinerary. I've already included the usual Shibuya/Ueno/Shinjuku/Harajuku visits so my brother can also experience them. However, I'm wondering if there are unique or "hidden gem" places in Tokyo you'd recommend, so both of us can have "first time experiences".

They can be parks, buildings, temples, or just about anything, even restaurants.

Thank you!