To create Type C Relics and Leons you will need to visit the Hero at your HQ. It is recommended that you do this before attempting upgrades as it vastly increases your chances of success.

Relics

55 Relics require two stages to go from Relic grade to Type C:

Relic to Leon: 55 Relic + 99 Keens + 99 Keens + 99 Keens + 200 million race currency

Leon to Type C: 55 Leon Relic + 99 Keens + 100 million race money

Leons

Luckily Leons only need 1 combination to go to Type C.

Leon to Type C: 55 Leon + 99 Keens + 100 million race currency