Like I said, you'd need to sacrifice 4 4* champions or chickens to rank Kael up to 5*. It appears that you lack 1 more 4 star champ (but you can just rank up the level 30s for this). You also need to unlock the champions first before they can be used as fodder.
For visual reference:
PS Avoid using epics as food as much as possible lmao, I don't have food champs at the moment so I just had to show how it's supposed to look like.