Hey! Sorry it took so long for a response to this. Not sure if you are still looking, but if so, perhaps can direct you to some sources. Unfortunately, there is not a great introductory read that focuses solely on the Sengoku period. This doesn't mean your completely out of luck, as there are some books that cover a bit more than just Sengoku, that would be a good start to the topic, even if you just skip to those sections. One such book I would recommend is Kathe Roth's translation of Souyri's The World Turned Upside Down: Medieval Japanese Society. It covers Heian period through Sengoku. Has a narrative structure, which provides an engaging read. Goes into a bit more of the social, economic, and cultural aspects of the periods than you might see in other introductory level books, giving you the context to help inform the narrative history.

Along with this, you might want to check out r/AskHistorians booklist here. There are several other book recommendations that might serve as a nice follow up to an introductory read. Something like Japan Emerging: Premodern History to 1850 or Japan Before Tokugawa: Political Consolidation and Economic Growth: 1500-1650 (both listed in the booklist), which take the form of standalone essays about various topics, might be the place to look next. There are other books that follow the same form that you could look into as well, such as The Bakufu in Japanese History (edited by Jeffrey Mass and William Hauser) or War and State Building in Medieval Japan (edited by John A Ferejohn and Frances Rosenbluth).