Based on the title, one of the main characters is likely the 'yankee'. And the other important character would be the'seirei' (the spirit) who loves the Yankee in the isekai world. But there could be other supporting characters that we don't know about without reading the novel.
The title 'yankee wa isekai de seirei ni aisaremasu novel' gives some clues. 'Yankee' might be a unique type of protagonist. The 'isekai' part indicates a different world setting. And 'seirei ni aisaremasu' means being loved by a spirit. It could be a story about a Yankee's adventures in a new world where a spirit has special feelings for them. There could be elements of discovery, relationship - building between the Yankee and the spirit, and maybe challenges they face together in this strange new isekai world.
I'm not entirely sure as I haven't read it specifically. But generally, in this kind of 'isekai' (another world) themed web novel, it might be about a 'yankee' (which could refer to a certain type of character, perhaps a tough or delinquent - like one) who gets transported to another world and is loved by spirits there.
I'm not sure specifically what 'inkya no boku ni batsu web novel' is about as it's not a widely known title to me. It could be about various things like a personal journey, a fictional adventure, or a unique relationship. Maybe it has elements of mystery or drama.
There are several web novels that share some elements. 'Re:Zero − Starting Life in Another World' is somewhat similar in the sense that the main character is in an isekai setting. Although the character isn't a 'yankee' type, the theme of facing challenges and forming relationships in a new world is there. Also, 'Sword Art Online' has an element of being in a different world (virtual in this case) and dealing with different entities, which could be related to the overall theme of the given web novel.
The 'Team Yankee Novel' is mainly about military operations and the experiences of the soldiers. It often depicts combat scenarios, military strategies, and the camaraderie within the military units. It gives readers a look into the world of military warfare and the challenges faced by those on the front lines.
The Team Yankee novel is grounded in a speculative scenario of a large-scale military conflict. It imagines a different outcome and course of events compared to real history.
Yankee Doodle has a long history. It originated as a British song used to mock colonial Americans, but Americans reclaimed it and made it their own during the Revolutionary War.