Ikebukuro is a great place all year round. The huge, indoor, shopping complex “Sunshine City” will keep you cool during the heat and warm during the winter. In the main street you’ll find many restaurants, game centers, cinemas and some shops like the Hello Kitty Store, ABC Market and Uniqlo.
In the Sunshine building you can find all kinds of entertainment. They have a observatory deck, museum, aquarium, planetarium, a Food Amusement Park called “Namja Town” and J-World, a Shonen Jump Magazine-themed Theme Park. You’ll also find lots of fashion shops, Disney, Sanrio and Ghibli stores and restaurants. You can easily spend the day in Sunshine building and still not see everything.
For information about the observatory, aquarium and planetarium, visit the official Sunshine City website (in English): http://www.sunshinecity.co.jp/english/
Official Namja Town Website: http://www.namco.co.jp/tp/namja/pdf/english_guide.pdf
Official J-Work website: http://www.namco.co.jp/tp/j-world/en/
Around the corner there is also “Otome Road” a street with many shops to buy Anime related stuff, mainly focused on woman though. You’ll find Animate, Mandarake, K-books and more.