Ichigo Kurosaki is an average high school boy with a not-so-average ability to see spirits - something that hadn't affected his life much until a strange woman entered his room one day. Named Kuchiki Rukia, she's a shinigami who was sent from the spirit world to destroy a hollow - a dead-soul-turned-monster; and much to her surprise, Ichigo can see her. When the hollow suddenly attacks his family, Rukia intervenes and is injured in the process, leaving Ichigo to fight it himself. But when Rukia lends him her shinigami powers - which is forbidden - he inadvertently drains them away and has no way to return them. Now, Ichigo is a full-fledged shinigami who must juggle his studies with his newfound duty of fighting hollows; but having gained his powers through forbidden means, the spirit world isn't going to leave Ichigo alone. Ichigo and Rukia must keep their situation a secret from the other shinigami, or the consequences could be dire.
Bleach and Shakugan no Shana are curiously alike. there is the supposedly 'normal' human guy who suddlenly gets attacked by the bad guys and gets saved by the mysterious girl/love inerest and then things happen and get epic. the only difference is the Protaginist in Shakugan no Shana is an Ichigo without the hero complex.
These two mangas are very similar. In both the main character is a short female tsundere and they come from a different kind of world. There is also a male lead that is kind of less powerful than the female. Overall, if you like one, you will like the other.