Okay, I'm going to walk you through what happened while playing, and see if someone can help me.

I am defender

One attacker declared, one defender declared

Edge Battle occur, I play a Fate card that deals one damage to a participating unit

I damage and destroy his one attacking unit

So now I have my defender unit, with no attackers. What can I do with it? There's nothing else participating in the conflict, can I attack a non-participating unit? Can I attack one of his objectives? Or do I just not get to do anything since there's no participating unit? 

you focus your defender to strike

then resolve your combat icons

as the defender your blast icons are ignored

as the only participating unit you can only used targeted strike to deal damage

the attacker doesnt get the unopposed bonus

the engagement ends

Okay, so without targeted strike, I don't get to so anything with that unit. 

Since there's nothing I can strike, do I have to ready to strike and take the focus token at all? Seems odd to penalize my unit for not actually doing anything. 

jivjov said:

it is the cost for commiting a unit to the engagement

how are you being penalized? you chose your defender and you chose to play that fate card

also you can only play fate cards if you have a unit in the engagement 

you defended and thus could play cards into the edge battle and your opponent did'nt get the unopposed bonus - ergo your unit actually did do something

It feels like a penalty because instill have to exhaust a unit with a focus token even though I played the edge battle well enough to actually destroy all attackers. But of those are the rules, oh well. At least I know, the rule book didn't make it very clear. 

dbmeboy said:

And if the defending unit has multiple tactics icons, the controlling player can decide how to distribute the tokens.

jivjov said:

It's very clear that no unit can leave an engagment ready. It must be focused. You're not being penalized, you won.

 Concur with above few posts. You win the battle and might be able to additionally focus opponent's units. If you are defending, the focus token placed will be removed on your turn. Sounds pretty good to me. 

Agreed completely, the rules are very clear.