I had the chance to take a walk with a friend through Showa Memorial Park in Tachikawa today. I was pleasantly surprised to see the cherry blossoms were in better bloom than I had expected.
The park is a great place for lots of activities. There are rental boats, rental barbecue areas, a waterpark, lots of amusements for kids, a frisbee golf course, many places to eat, miles of bike paths, fireworks in the summer . . . it's a great place. Admission for adults is ¥450. The nearest station is Nishi Tachikawa but you can get there from Tachikawa, Higashi Nakagami or Musashi Sunagawa stations.
Check these links for the lowdown. Look carefully. There are days admission is free!
https://www.showakinen-koen.jp/guide-english/schedule-english/
https://www.showakinen-koen.jp/