Short answers, pulled from the story.
The name Ikebukuro literally means "pond bag" in Japanese, derived from the kanji for pond (ike) and bag (fukuro). A plaque near the west exit of Ikebukuro Station explains that the area once contained multiple lakes, giving rise to the name.
Ikebukuro Station is the third-busiest railway station in Japan and ranks among the world's busiest stations. It is served by JR East lines, the Seibu Ikebukuro Line, and the Tobu Tojo Line.
Sunshine City is a large shopping and entertainment complex that opened in 1978, built on the former site of Sugamo Prison. It includes an aquarium, a Pokemon Center, and cat cafes, and is anchored by Sunshine 60, which was the tallest building in Asia at the time of its construction.
Frank Lloyd Wright designed Jiyu Gakuen Myonichikan, a school in the Nishiikebukuro district, which was built in 1921. The building is open to visitors today.
Ikebukuro is home to a Chinese community that developed from the 1980s onward, creating a district of Chinese goods and services that attracts tourists. It is smaller and less populous than Yokohama's Chinatown, which lies to the south of Tokyo.
The light novel, anime, and manga series Durarara!! is set in Ikebukuro, as is the manga and TV drama Ikebukuro West Gate Park. The district also appears in the Megami Tensei video game series and in Lost Judgment.