Flowers and Deities lets either army’s losses pay for your next spell

Losing a soldier and gaining a resource happen together in Flowers and Deities. The official description says every lost unit fills the blood pool, whether it belongs to your army or the enemy. Spells and summons spend that pool.

The player can also sacrifice friendly soldiers when the arena runs dry. That turns a casualty into something you may deliberately choose, rather than only a failure to prevent. The exchange has two visible sides in the advertised rule: a unit leaves the army while blood becomes available for another intervention. No yields or prices are supplied, so the source does not establish that a particular sacrifice is worth more than the soldier’s continued contribution.

Formation, equipment and recruitment still determine the army entering the auto-battle. The blood pool gives the fight a second resource to watch after that preparation. If the premise appeals, the consequential question is whether you want to decide that one part of the army should be spent to change what happens to the rest. A filled pool can be useful; how it became full remains part of the cost.