Basic Info:Katana is great champion, she distribute lots and lots of damage and have exelent life and move speed, wath mae she the perfect choice to pla as a bruiser/assasins.
Artifacts : well start picking Soultaker Katana, then Velocity 9, Deathstroke Claymore, then Batman Utility Belt, Amulet of Isis for extra life move spped and cooldown reduction, and for last huntress Crossbow.
Too amplifiers pick wathever you thing is good, but remeber to pick augments and mods relationed to bruiser/assasins role - move speed,atack damege/speed,health,cooldown reduction and critical chance -.
Stolen Powers : Her invunerability is awsome, so you can let there, or you can pick Doomsday Invunerability or Supergirl Invunerability, also you can pick Krypto Healing Wave or Poison Ivy Healing Wave, or if you prefer Flash Super Speed.
Gameplay : Focus to upgrade your Q,E and your Ultimate R, also remeber to upgrade your passive, for last upgrade your W. To get more kills just play as a Assasins and remeber to use your W to get close to enemies, then use Q to damege then and E to deal more damage, if possible use r to hit multiple targets, but be carefull because they can go to turrets or close to more enimes, so thiink wice before use it. Also you can go jungle if you prefer, but she work better in bot lane with a ranged champ.