You must pick a class of honour. Here's your options:

Samurai
Classes:
Spy
Pyro
Demo
Soldier
Cosmetics:
There are actual samurai cosmetics for each of those classes, but you could just be lazy like me and equip the hong kong cone, and I don't feel like tracking down their names.
Weapons:
Spy:
Conniver's Kunai
L'etranger
Red Tape Recorder
Pyro:
Any primary
Any secondary
Neon Annihilator
Demo:
Ali Baba's Wee Booties
Splendid Screen
Half Zatoichi
Soldier:
Any primary
Concheror
Half Zatoichi

Ninja
Classes:
Spy
Engineer
Scout
Cosmetics:
Same cosmetics (hong kong cone) , except scout needs to wear the ninja set
Weapons:
Spy:
Same as Samurai.
Engineer:
Any primary
Any secondary
Any melee that can Ninjaneer
Scout:
Any primary
Flying Guillotine
Three Rune Blade

You're not done yet. You must follow the samurai code.

1. Do not kill friendlies in community servers.
2. Always kill friendlies in other servers.
3. Kill anything in your way.
4. Follow the code.

You're not done yet. You must follow the code of honour.
1. Never kill friendlies in community servers.
2. Always kill friendlies in other servers.
3. Never be seen.
4. Follow the code.