What does “initial rarity of R” mean?

Characters with an initial rarity of R are those whose base rarity is R when being obtained through invocations or other means.
Characters with an initial rarity of R have the following characteristics:

• Normally, they are obtained through invocations with a rarity of R.
• In other select cases, such as when the character has been set in an invocation’s Wish List, there is also a chance that they may be obtained at a rarity of SR.
• They may also be obtained at a rarity of SR when using items where you are guaranteed to get SR characters.
• In the Character Index, they will be displayed under the SSR+ category.