The Crescent of the Sun is a relic found in The Darkness II. It's a talwar said to be created from a drop of the sun's flame.
The Crescent was wielded by The Angelus, who believed that this sword will permanently destroy The Darkness, but she didn't get a chance to use it; upon carrying it into battle against The Darkness, The Angelus was immediately disemboweled. Years later, the Crescent was found by a holy warrior. When he wielded it against The Darkness, he managed to get a few good swings, but the Crescent passed through The Darkness. Later, a group of monks found the Crescent and tested it on multiple targets, only to discover that the Crescent phases through all matter.It's possible that only The Angelus can wield the Crescent for it to have any effect, but since The Angelus didn't try to reclaim the Crescent, it's also possible that The Angelus eventually abandoned the Crescent when she found out that it just phases through all material.