I can already see sei going back home and potential wife clamoring around him then he introduces the mc as a good friend and the others go jealous and all that crap.
"Who is she?""How dare she think she can be his friend!""What right does she have to be so close to the Crown prince!"and so on....
Boom MC summons 2-4 Sacred Beast and shuts them all up.
Glories!
So the cat is the next one to befriend her? Might as well get a cute demon cat. There are a lot of stories of cute lovable demon animals befriending the main character.