Saika is an ancient, powerful entity that manifests itself as a cursed Japanese sword. It has an extreme love for humanity, and, like how humans might express their love by hugging or kissing, Saika expresses its love by cutting and possessing people. Its ultimate goal is to take over all of humanity. When under Saika's influence, a person's eyes glow red, often with a crazed, wide-eyed look. It is also possible that humans get a boost to their strength and fighting abilities when possessed, allowing normal people like Anri to go one on one with Celty Sturluson.