dow.rb(date)

This code defines a constant DOW_JP representing the days of the week in Japanese (日曜日, 月曜日, 火曜日, 水曜日, 木曜日, 金曜日, 土曜日).

Execution:

DOW_JP = %w[日 月 火 水 木 金 土].map(&:freeze).freeze
#=> ["日", "月", "火", "水", "木", "金", "土"]

Executed with Ruby 3.3.5