It's an unfinished concept volume that's been made obsolete by the author's later remake of the franchise. The only reason to read it is to understand how the successors improved upon it. With a barely existent plot and bare-bones characters the appeal of the manga past being a predecessor is pretty slim. The interactions between the characters can be enjoyable but anything spectacular is cutoff with a cliffhanger. Checkout the remake manga and the 2nd anime adaptation. But unless you want to "experience everything" of the franchise, I'd not read this. There's a OVA adaptation of this that you can watch anyway.