Yuubae Sakusen

One day during class, high schooler Suzuka Shigeru got a text message from his classmate, Kazama Akio. The text message read "I have something interesting to show you." Having no idea what he wanted to show him, Shigeru visits the Kazama residence.

The Kazama residence is huge and looks to have a lot of history behind it. Akio takes Shigeru to a cluster of three "Torii" (Japanese Shinto gates) in the huge backyard of his mansion. At sunset...when the shadows of the three gates merge, a shining beacon of light forms at the cross section. Out of curiosity behind this mysterious phenomenon, Akio pushes Shigeru and himself through the beacon of light. Next thing they know, they end up in the Edo period of warring Japan, in between the battle between the Iga and Kazama Ninja clans...!

(Source: MangaHelpers)