Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This build is a pretty good build for quick assassin kills. Based on ability power, the shunpo is just crazy and the Death Lotus are just crazy.
Wait until you know against who you are in the lane. If your opponent is a tank or as a long attack/spell range, take bouncing blade as your first skill, so you can push him.If not, you better choose shunpo to make quick attacks. As you level up, you will now start harrassing by a shunpo, then immediatly a bouncing blade to make high damages. Wait until you have 1235 gold to return to the shop for the meijah's (because Katarina is a early game killer, try to get it as soon as possible). When you are level 6, you are ready to do a lot of kills. Shunpo, then Death Lotus, then bouncing blades when is attempting to flee.
When you have reached level 9 or 10, you can start to jungle between lanes to make easy kill. You will see that qith this build, you will be really strong when your meijahs is stacked. You will be probably to buy the Zhonya's Ring in mid game. When you have it, your ability power will be 25 percents better + 120 ability power, so you can reach near 400 even 500 ability power.
At the end, if you have between 350 and 500 ability power, you can shunpo easily between 2 or even 4 champions, then do a death lotus. I even did a pentakill once so... Remember that ennemy stunners like amumu or scion will absolutely kill you if they stun you, so watch your back and make the jungle your territory.