Hey, name's Aeggy, have been a member of this site for like 5 minutes and I'm making this guide because I'm bored

I have played 2 to 3 games of Kappadin this week, don't worry, I'm reliable.

Now, pretty sure I don't need to say this for every champion that uses Tear of The Goddess but, well, rush it
The moment you have 850 gold go back and use that purple F key (or D if you are a pleb) to get back to lane
I mean, you COULD go back with like 1250 to also get a ruby crystal for more survivablity which builds into Catalyst but that's for plebs, and since I used it in a negative connotation before you should realize that my opinion on plebs is not positive
Kappadin is no Karthus boy, you won't fill this tear of salt in 3 miliseconds but if Kapps has something in common with Karthus is he dont give a **** and he'll look like a dumbass doing it, just spam abilities and riftwalk your way to lane when TP is not up, who needs mana? Well getting into that...

Heh, well, yeah, here's out objective.
If you're getting tired from the overuse of commas, well, how unfortunate.
When you play this build we're aiming for at least 4000 to 5000 mana boy, less than that is blasphemy
You will need to be able to just press R all the way to the enemy nexus and have half mana when you get there.
Now you might realize that on this chapter I'm properly indenting my paragraphs while on the other one I wasn't, well I just realized that now and I'm too lazy to fix it, so back to the point.
Now, I just googled Kassadin and apart from realizing that the fandom wiki does a better job at posting their ability ratios than the official site, Kassadin's R scales with 2% of your maximum mana, 6% fully charged, with our previous example of 4000 mana that brings us to 240 bonus damage per jump just for the mana, now that number isn't impressive at all, but posting the math makes it impressive, also, this 240 damage also applies to our autos because of Muramana, except that with physical damage.

TL;DR: mana = damage = fun = an accomplished feeling of giving time an attention to a hobby and/or addiction you thoroughly enjoy

The usual answer is you don't, but since I dedicated 20 minutes of my life to this I'll expand on it
You go to lane, you farm for an hour, you win....
I wish that was part of the sarcastic nature of this guide, but that's actually it, when you finish your Seraph's you will actually be able to assist your team by doing decent damage but you don't give a fruck about that, you keep farming and farming, seeing that CS number go up should give you an incomparable sense of accomplishment as you steal the entire jungle of your 0/7 Warwick, eventually some random ADC will run into you and you will just R into him/her with only 2 stacks and one-shot them and then you will realize "oh **** im kind of strong", then you run into the enemy base and tank their turrets as you destroy them in 3 hits and win, that's the nature of this build;
Get a robot to play the game for you while you play country roads in the background and watch some hentai and eventually you will be unstoppable. You never run out of mana and Gathering Storm with Rabadon should make up for the lack of actual AP items in your build as you mow down anyone in your path.

Hope you enjoyed this guide as much as I will enjoy this ham and cheese sandwich with mayo and ketchup I'm about to eat and utterly regret