Ruby

Rubies are the premium currency in Mario Kart Tour. Prior to the Battle Tour, they were mainly used to summon new drivers, karts, and gliders from the pipe. Five were required to fire it one time, although 45 could be spent to fire ten at once. As of the Battle Tour, rubies are instead primarily used to redeem High-End drivers, karts, and gliders from the Spotlight Shop, with drivers costing 150 rubies each, and karts and gliders costing 100 rubies each. In addition, since their introduction in the Mii Tour, rubies can be spent to redeem Mii Racing Suits, costing either 70 or 100 rubies each. If the player does not have any or enough Coin Rush tickets, rubies can be spent to play Coin Rush, with 5 rubies multiplying the coin count by 2, 15 by 6, and 25 by 10. In addition to being purchasable with real money, rubies are obtainable in-game through Tour Gifts, by completing the game's Standard Challenges, as an occasional daily reward, from Event Shops, and as a reward for reaching certain levels and achieving high ranks in a ranked cup (the amounts for the latter varying depending on the player's current place and tier). In the pre-release beta test, rubies were emeralds and could not be purchased. The front part of a ruby resembles an Item Box.

In-game description
"You can use these to fire off the pipe or play Coin Rush."

Names in other languages
Rubino