Specifically, I’m looking for a word that would imply readiness, if not giddiness, for a battle, fight, or war. In this particular instance, this person has the odds against them but is absolutely ready, with a smile on their face and determination in their eyes.
Example:
I looked over and – just from a brief glance – knew that he was ________________.
Fired up means emotionally, and to some extent, physically ready for action. It's very similar to @RichardKayser's 'pumped'.
How about pumped or ready to roll?
From The Free Dictionary:
pumped: emotionally excited; enthusiastic or eager
ready to roll: prepared to start doing something
Your example:
I looked over and--just from a brief glance--knew that he was pumped.
I looked over and--just from a brief glance--knew that he was ready to roll.
Both of these "imply readiness, if not giddiness, for a battle, fight, or war" and a person who "is absolutely ready, with a smile on their face and determination in their eyes".
If you are looking to expressions more sophisticated than "combat-ready" or "ready to fight", consider "on a war footing", even if it generally used for a group (country, army, company, ...).
Definition: the condition of being prepared to undertake or maintain a combat.
Example: I think I'll approach it differently than, you know, say, my dad who had, you know, had a very - what's the right word for it? - a very - he was perpetually on a war footing with, you know, with the world.
I think bellicose may fit in your context:
- demonstrating aggression and willingness to fight.
and combative:
- ready or eager to fight; pugnacious.
Oxford Dictionary
I'd say, spoiling for a fight
be spoiling for a fight
to be very eager to fight or argue He says what he thinks, and so people think he always seems to be spoiling for a fight.
He was "keen" for battle - ready, eager, and enthusiastic - blind to their disadvantage and the bloodiness of war.
Hardened: made or became more severe and less sympathetic.
Hardened: having developed a way of dealing with bad experiences so that they no longer upset you :
What about "embattled"?
From Webster's Revised Unabridged Dictionary (1913) [web1913]: Embattle \Em*bat"tle\, v. t. [imp. & p. p. {Embattled}; p. pr. & vb. n. {Embattling}.] [OF. embataillier; pref. em- (L. in) + F. bataille battle. See {Battle}, and cf. {Battlement}.] To arrange in order of battle; to array for battle; also, to prepare or arm for battle; to equip as for battle.
