Note this guide is not the latest one there is a bug. It's not supposed to look like this
His best core item is NOW bonesaw
Why it synergies his passive well allow him to kill tank effective
The stats overall give gives everything to him.

Note that you buy can tension bow as first item as long you have a high a pure weapon power stat. Poison shiv is good first item very cheap allows you to counter healing and sustain. Feel free to explore more item you think has a powerhouse spike on kensei.