Day 1
Old Tokyo: Asakusa, Ueno, Akihabara
Morning
Sensō-ji at opening (around 06:00 — the temple grounds never close, but the shops on Nakamise open at 09:30). Walk through the Hōzōmon gate while it's still empty. Climb to the Asakusa Culture Tourist Information Center observation deck (free, 8th floor) for the best top-down view of Sensō-ji you'll get without paying.
Afternoon
Walk or train one stop to Ueno. Ueno Park is the city's largest, with the Tokyo National Museum, Ueno Zoo, and Shinobazu Pond all clustered. Pick one museum (the Tokyo National is the right answer if you have to choose) and spend 90 minutes. Lunch at a tonkatsu shop near Ameyoko market.
Evening
Akihabara Electric Town. Yodobashi-Akiba is a 9-floor electronics megastore — go even if you don't intend to buy anything. Dinner at one of the standing-bar tachinomi under the JR tracks. Be on the train back to your hotel by 21:30; tomorrow is heavy.
TipAsakusa is one of the few Tokyo neighborhoods where a yukata rental for the day looks appropriate rather than costume-y. Several shops on Orange Street offer them for ¥3,500–5,000 with hair-styling included.