The Honor Halo represents a great achievement that you've made! It is harder to acquire than you would think, and only the strongest warriors will attain this honor!
There are 5 ways to obtain an Honor Halo:

1. Guild War:
The Guild Leader and Deputy Leaders who won the Guild War that week can speak with the Guild Officer (Guild Map, 44 60) to claim their Honor Halo!
The effect of the Honor Halo will last up to 7 days, after being claimed.
There will be a Halo for the Top Guild Leader and 6 Top Deputy Leaders.

2. Weekly PK War:
The winners can claim their Honor Halo when they are transported to Twin City.
The effect of the Honor Halo will last up to 7 days, after being claimed.

3. Monthly PK War:
The winners can claim their Honor Halo after they are transported to Twin City.
The effect of the Honor Halo will last up to 30 days, after being claimed.

4. Class PK War:
The winners can claim the Honor Halo for their class: Top Archer, Top Ninja, Top Trojan, etc.  
The effect of the Honor Halo will last up to 7 days, after being claimed.

5. Couple PK Tournament:
The winners can claim their Honor Halo after they are transported to Twin City.
The effect of the Honor Halo will last up to 7 days, after being claimed.

Note:
1. Each player can have only one Honor Halo, at a time. If you have the opportunity to have more than one, there will be a confirmation message that asks if you want to give up your current Honor Halo and replace it with the new one.
2. The winners must claim their Honor Halo before the next contest begins, or it will be forfeited.