Three physical cards are on sale for Japan. This compares how the options are structured, not price or speed. Allowance, days, and price are whatever the option you open says on its product page. The shared activation order is in after the card arrives.
SoftBank: Japan, plug and play, on every option
Every SoftBank option lists coverage as Japan and activation as plug and play. The options differ by allowance, which is written on the option name. It is not repeated here.
KDDI: a blank card and day plans are different paths
KDDI lists a blank card and several day plans. The day plans say plug and play. The blank card's Chinese activation says it starts on arrival, and its English activation field is empty. The summary line about buying a blank card first describes one path. It does not describe the day plans. Speed tiers are on the options; this article does not repeat those figures.
Rakuten: a new card is not a renewal
Rakuten coverage is a multi-country list, not Japan only. New-card options say plug and play. Renewal options say online top-up and do not ship a card; they are for someone who already has the card. Read whether that row ships a card or only recharges one.