By default, the XP formula is 12 * (level * level) + level * 12. This means that when Kiai is calculating how much XP is needed for level 10 for example, it will calculate 12 * (10 * 10) + 10 * 12 which is 1320. This means that level 10 requires 1320 XP to reach.
You can make your own formulas like that and use the placeholders listed on the command as variables