Hi, my name is Luna1337, as is my ign, and I main Katarina. She is my favorite hero and I have been playing her for quite some time now. She is by far the most versatile champion with the best choice of option for her build to be AD/AP. I choose this because 2 of 3 of her skills scale with both with one of those being her ultimate. So going pure AP will fuel 3 skills but will not be as efficent for her AD/AP scaling skills, so some AD is the way to go.

I recommend laning mid as your runes will come in handy here if laning against that squishy carry the other team has. Although if you could not go mid, laning with a partner is just fine too but will need you to ks and last hit more just for the first half of the game and play carefully. With this build, I would be careful to take the 1v2 lane if you have a jungler on your team as you are still squishy early game and depending on who you are laning with could turn out bad for you.

I take mostly magic pen as all her skills deal magic damage for marks and quints. For seals I took evasion to take advantage of your nimbleness mastery and as a defense against AD champions. For glyphs I took the flat magic resist for that early and possibly through out the game advantage against that AP carry you would face in mid.

I take the 9/21/0 to make up for her squishyness (if that's a word) and take advantage of nimbleness as well as ardor, not to mention the defensive mastery combined with her killer instincts active on shunpo. I also took the archaic knowledge in the offensive tree.

I start out with boots and 3 hp pots for hit-and-run tactics early game and then rushing sorcerer boots for very easy squishy kills in mid and other lanes. Then grabbing the spell vamp hextech revolver so you could lane and farm better with some huge healing on your ultimate too. Then advancing onto hextech gunblade, DO NOT FORGET THIS ITEM'S ACTIVE hextech gunblade's active is very strong and should be used at every opportunity. 700 range, 300 magic dmg, and an awesome slow, you'll need this through the game for that nuke burst or if you are chasing down someone. Rylai's is next with its very important staple slow, big AP boost, and very much needed HP boost. Next you take rabadon's deathcap for the obvious reasons of the huge, possibly OP? o.O, AP boost it gives. Abyssal Scepter is next giving magic resist, AP, and more magic pen. Last, you could choose either between Lich Bane, or Zhonya's depending on the opposing team. Need armor? go for Zhonya's, wanna destroy squishys with a basic attack? take Lich Bane.

Ghost and ignite, plain and simple. Giving great focus power as well as escape/chase ability, I do not see why you would choose anything else. Cleanse is out of the question because if you are shut down during your ulti, run out of range during a team fight and just hope to get 2 ***its or kills for the auto refresh on it and you shouldnt need that hardcore of defense if your team is each doing their roles. Kat is a very offensive and versatile champ, so she should need offense.

Ionian boots of lucidity are a good choice for boots but now for me, I would rather take better burst damage over cooldown reduction, I say let your passive take care of cooldowns as well as blue. Better burst damage=more kills/***its=less cooldown, but more cooldown=more kills/***its but not better burst damage and squishy kill potential. I also dont run mejais because I do not like the risk you take with it and would go with much more stable items.

I also with though that I could know how to make this build much more visual but I lack the knowledge of being able to show items images and such.

Thank you for reading and I hope this helps for you and will post positive things.