Question 1

Where is Toshimaen?

Accepted Answer

Toshimaen is in Nerima, Tokyo, Japan. You can see its exact position from the map coordinates and the Street View link.

Question 2

Which scene of Negative Positive Angler does Toshimaen appear in?

Accepted Answer

Toshimaen appears in EP2 of Negative Positive Angler.

Question 3

Can I visit Toshimaen?

Accepted Answer

Yes. Toshimaen is a real place you can visit. Check what it looks like on Street View before you go.

Question 4

Where was Negative Positive Angler filmed?

Accepted Answer

Anime and manga are not filmed the way live action is. Their backgrounds are painted from photographs of real locations, and Toshimaen is one of those real places (EP2).