Rarity
Card Rarity or simply Rarity is a card property that determines the chance of the card being pulled in a Transient Summon, as well as how Sacred Artifact Levels a card gets when a duplicate is pulled. It also determines the level caps of a card, and is also strongly associated with the cost and the CS damage multiplier. Rarities 1 through 5 exist, denoted by the number of stars (☆) paired with the card.
Utility
Cards with higher rarities often have superior skill kits compared with those of lower rarities. However, this is more a general rule of thumb than a strict correspondence. For example, early-release ☆5 cards such as 
Claude are notorious for having mediocre kits, of which many other cards of the same and lower rarities can easily outvalue. However, higher rarity cards are apparently more likely to receive exclusive skill evolutions that can drastically improve their utility. These include but are not limited to 
Ophion's Primordial Wyrm Reincarnate+, 
Duo's Fount of Wisdom+, and 
Eita (Set Sail)'s Sea-favored+.
Transient Summon and Rarity
Within a Transient Summon, the probability of any card of a given rarity is as tabulated below:
| Rarity (☆) | Single Summon Rate (%) | 10 Summon Rate (%) |
|---|---|---|
| 3 | 80 | 0 |
| 4 | 18 | 96 |
| 5 | 2 | 4 |
When a card duplicate is pulled in either the Transient Summon or Ally Summon, the amount that card increases in Sacred Artifact Lv depends on its rarity, as tabulated below:
| Rarity (☆) | Sacred Artifact Levels Gained |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 5 |
| 5 | 20 |
Rarity-dependent level limits
A card has several level caps, or limits, and these limits depend on the rarity of the card, how many times the card has had their limit broken, and how many level seeds were invested in the card's associated unit. These level caps are tabulated below:
| Rarity (☆) | Limit Break Stage | ||||
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 (unseeded) | 3 (fully seeded) | |
| 1 | 20 | 30 | 40 | 50 | 60 |
| 2 | 25 | 35 | 45 | 55 | 65 |
| 3 | 30 | 40 | 50 | 60 | 70 |
| 4 | 35 | 45 | 55 | 65 | 75 |
| 5 | 40 | 50 | 60 | 70 | 80 |
Association with Cost and CS multiplier
Rarity strongly predicts the cost of most cards, with some exceptions. This relationship is tabulated below.
| Rarity (☆) | Cost | CS damage multiplier |
|---|---|---|
| 1 | 2 | 2 |
| 2 | 4 | 2 |
| 3 | 8 | 2 |
| 4 | 16 | 3 |
| 5 | 24 | 4 |