I've seen this once about 10 years ago and been searching for it since. I could draw the look of it but can't remember the name or find it on Google.
This is a Japanese anime movie, not series, probably made in the 1990's. It features a special unit of the police or military and a rogue operator who fight these giant floating, demonish creatures using hand held, cannon like spell casters.
The protagonists have an assistant who covers their bodies in mystic runes/script before putting on a high tech hard suit. They then use a giant hand held cannon which materializes their combat spells as floating, mystic circular disc's of glowing lines and symbols right at the ends of the barrel. I believe that after firing off a spell, their suits would eject a number of glowing power cells depending on how powerful the spell was.
Most of the scenes take place at night and are quite dark. I believe there's only 2 or 3 of the spell guns users in the movie. The rogue operator travels in his own truck/van which carries his suit, weapon and assistant. He and the governmental/police combatant are pretty hostile towards each other.