Yes, it can be quite common. In Japan, there are many cafes where people like to relax and read. The concept of 'isekai' is very popular in Japanese media, so an 'isekai kissa' might attract customers who are interested in that kind of fantasy world while enjoying their coffee and a good novel.
I'm not sure specifically as I haven't read it in detail. But generally, 'isekai' often involves a character being transported to another world. Maybe this light novel is about an after - school quest in an isekai setting.
Since the details about this light novel are not widely known to me, we can only make assumptions. It could be that the main character is a high - school student who is quite ordinary in the real world but discovers extraordinary powers or abilities in the isekai world after school. There might also be a mentor - like figure in the isekai who guides the main character through the quests, and some interesting villains or rivals that the main character has to face during these after - school adventures.
You can expect a very relaxing time. Having coffee while reading a novel in such a place might give you a chance to escape from the daily hustle and bustle. The coffee aroma can enhance the mood, and the novel can take you to different worlds, just like the name 'isekai' implies, which often refers to another world in Japanese media.
I'm not sure specifically as I haven't read this light novel. But generally, 'koi' means love in Japanese. It might be about a love story that has something to do with twins ('futago'), like perhaps a love triangle involving twins that can't be separated ('warikirenai').
The 'yuuki yuuna wa yuusha de aru visual novel' mainly focuses on the story of some brave girls. These girls are ordinary at first but are gradually drawn into a heroic journey. They experience a lot, like fighting against mysterious enemies, and at the same time, their friendship is deepened during these processes.
One characteristic is the isekai setting. The protagonist is transported from their normal world to a different, often magical world. Another is the use of magic. The characters usually have to learn to control and use magic in various ways to progress in the story.
The 'yuuki yuuna wa yuusha de aru light novel' could be centered around Yuuki Yuuna's journey as a hero. It may include her initial discovery of her heroic abilities. Maybe she starts off as an ordinary girl and then something extraordinary happens that thrusts her into the role of a hero. The story could also involve her moral dilemmas as she makes decisions in the face of danger. There might be a cast of supporting characters that either help or hinder her along the way, and the plot might unfold through different arcs that show her development both as a person and as a hero.
Since I don't know the exact details of 'isekai ekisha no kissaten novel', it's hard to say for sure. But if it's an isekai novel, perhaps it has a unique setting like the coffee shop in the title. Maybe the coffee shop in the other world has some special powers or is a gathering place for different characters from different worlds.