Saredo Tsumibito wa Ryuu to Odoru

The story revolves around "jushiki" (lit. spell equations), the equations that govern the quantum constant "h" of action, change the laws of physics at the local scale, give birth to TNT explosives and poison gas, and cause incredible physical phenomena such as plasma and nuclear fusion. Two "jushikishi" (spell equationists) who use jushiki in battle are Gayus (who deals with bad luck with tact) and the beautiful but cruel sword-wielder Gigina. These two bounty hunters are caught up in a battle with dragons in the city of Eridana and in the intrigue of great nations.

(Source: Anime News Network)