Question 1

Where is Lake Hirose?

Accepted Answer

Lake Hirose is in Yamanashi, Japan. You can see its exact position from the map coordinates and the Street View link.

Question 2

Which scene of Botan Kamiina Fully Blossoms When Drunk does Lake Hirose appear in?

Accepted Answer

Lake Hirose appears in ED9 of Botan Kamiina Fully Blossoms When Drunk.

Question 3

Can I visit Lake Hirose?

Accepted Answer

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

Question 4

Where was Botan Kamiina Fully Blossoms When Drunk filmed?

Accepted Answer

Anime and manga are not filmed the way live action is. Their backgrounds are painted from photographs of real locations, and Lake Hirose is one of those real places (ED9).