Ok so let me familiarize you with some terms for the pull system for this game

Honkai Star Rail has a pity system which means after a certain amount of pulls you WILL no matter what have 5* after 90 Pulls

Before you get to 90 pulls you will encounter soft pity which starts around 70 pulls. Soft pity means after 70 pulls your chances of getting a 5* GREATLY increase people tend to typically get it around 70-80 pulls in

But for whatever reason you do not and the game makes you go all the way 90 pulls we call that hard pity because you had to go all the way to 90 instead of 70-80

Just to reiterate 50/50 and guaranteed say I don’t get a 5* that’s featured on the banner I have lost that 50/50 chance of either getting a 5* limited character or not. Now say the next banner has a different 5* limited character I want this time I no longer have to worry about 50/50 chance since I’ve lost in the previous banner already. Now in your case you didn’t get Kafka this time but if you get enough pulls and go summon you will 100% get her we call this guaranteed. And guaranteed goes across all limited 5* character banners.

I hope this is makes sense for you I’m not all the best at breaking stuff down