This is basically the continuation of "Silent Voice", and you must read the sequel before this.
With Silent Voice, we established that Imai likes Hikita and had confessed. The boys had shared a few kisses and conversations as Hikita realised that his admiration towards Imai might be love, and it wasn't until the end of Silent Voice that their relationship started to take off (with Hikita offering his body to Imai in a very awkward way haha).
Invisible Stars starts off right where Silent Voice left us: going into the depths of their relationship, slowly, beautifully, with many heart-felt moments. Also, their physically relationship takes off as the boys explore the boundaries of their love in such an innocent way. The pacing of their romance is matched with the overall pacing of the plot: slow, calm and seductive. I found this so enduring and came to like their heavy petting sessions matched with their little talks about the future of their lives after school.
The overall feeling of this story is relaxing, happy and warm. It was just a joy to read and I really took my time with this. Nothing dramatically happens. The boys go to school. Go to training. Go home and then repeat, and somewhere amongst all that the boys make-out and act as normal high-school friends by hanging out and enjoying life. You could argue that the plot is some-what boring, but I would just say it's relaxing and simple.
In my review for Silent Voice I talk about the art. I mention that it doesn't appeal to me, at all, but by now I have grasped the character designs and layouts enough to enjoy this manga to the fullest, however, I still stand by my original comment where I said that I think that the mangaka wasn't trying to win her fans over with the art, and that she was just trying to express a cute little story about the ugly guy and the popular guy.
This has been broken down into three volumes, and I can pretty much guess that the third volume will be about the boy's lives after high school; a continuation of their relationship after they graduate. Even though the events are very mellow, I am still eager to follow the boys relationship to the next stage.
The mangaka, Atsuki, really has captured a wonderful little romance between boys who love baseball, and I highly recommend this to anyone who likes a feel-good story that leaves you wanting more.
[Copied from my MyAnimeList review]