Arca War is a guild versus guild event fought over three contested obelisks. Registered guilds are dropped onto the battlefield at their own spawn points and spend the event tearing down towers they do not hold while defending the ones they do. Nothing is handed out on the field itself. What you take away is Trophies of Battle, and those are exchanged for the real rewards once the fighting is over.
The event runs once a week, on Wednesday at 20:00 server time, and lasts thirty minutes.
Registration happens with Jin, the Arca War NPC in Acheron. The guild master registers the guild first, inside a five minute window, and members then have a further five minutes of their own to sign on to the roster. Only one registered member is required for a guild to field a team, so a small guild is not shut out. Jin also handles entry to the battlefield once the event is live.
Ten minutes after the event ends, anyone still standing on the battlefield is moved back out.
Three Fire Tower obelisks are in play. Two of them stand in Acheron, one in the Alkmaar area and one in the Ubaid area (map 92). The third stands in Debenter (map 96).
Each obelisk carries a deep pool of health, so bringing one down is work for a coordinated group rather than a single player. An obelisk that has already been captured holds noticeably less health than an untouched one, which cuts both ways: the ground you take is cheaper for the next guild to take back off you. Holding what you have captured is worth as much as capturing it in the first place.
A destroyed obelisk does not stay down. It returns after a short delay, and the fight over it starts again from scratch.
The contested areas are not empty ground. Around the two Acheron obelisks, groups of elemental spirits spawn and keep respawning through the event: Undine, Salamander, Sylphid, Gnome and Hellraiser. Debenter fields its own local creatures instead, Sellihoden, Ukanva, Silla, Normus and Muff. They are a nuisance while you are working on a tower and a real problem if an enemy guild catches you in the middle of a pull.
Taking part earns Trophies of Battle. They are paid out on the strength of what you contributed during the event, and the results screen at the end shows your contribution, your kill points and the trophies you walked away with.
The trophies are not the reward themselves. Afterwards you hand them back to Jin and exchange them in tiers, from a small turn-in at the bottom up to a large one at the top, and the tier you pick decides what the exchange is worth. Saving trophies is worthwhile. The smallest exchange gives a single draw from the reward pool, every tier above it draws more than once, and the size of the stacks you receive climbs steadily as the tier goes up. The largest exchanges also upgrade the headline Ruud payout to the bigger box. The exchange is a combination, and the client shows you its success rate before you confirm, so read that line before committing a stack you have been saving for weeks.
What the pool contains: upgrade and refining stones for Guardian and Mastery gear, Elemental Runes, Bless of Light, Steel of Heaven, Golden Sentence, Sealed Stone Shards, Guardian option change pieces, generous stacks of Pandora Picks, and a Ruud box.
Quantities are deliberately not listed here. The reward values are still being tuned, and a printed table would be wrong within a patch or two. The pool above is the honest answer to what you can get; how much of it is a moving number.