?
You main you raise its rank?
As far as I know in Ryuji's confidant after you reach a certain level you need to wait for him to contact you again twice before ranking up, one when he said he's trying to find a new place to train and the other when he said he's trying to find where Yamauchi drinks so he can snoop on him.
During those moments, Ryuji's confidant are greyed out even if you have enough points to level it up to the next rank.
The same happened with Kawakami, Futaba, Hifumi, etc etc where you need to finish their respective mementos quests first before being allowed to proceed, theirs will be a greyed out UP! icon before you finish those quests, or when you need to raise your social stat to the required level for those that block you with that.