Among the poorly documented things in RAID are the gains a champion gets for each Ascension star. Most of the time it is very small amounts of HP, Attack and Defense, but sometimes there are significant exceptions or deviations.
Here I am sharing with you an example of Versulf the Grim as I ascended him to the full Rank 6 or 6 stars. You can see from the picture that (and this happens only for the last star) he gains additionally:
- +20 to Resistance
- and +10 to Accuracy
This is significant as he already starts with 50 RES and 10 ACC.
So remember that this exists in the game, but it is not documented so you cannot lookup Ascension per star information for your champions.
However, if you look at the Champions Index you will be able to see there the final stats of a fully upgraded champion, so while you cannot know what you will get on which star you can find out the final result.