The first thing to know about First Love is that it is neither romantic nor a comedy. The title is terrible, even though it is relevant. First because it is misleading, which is not helped by the promotional art that looks romantic from a distance. Second because it is far from unique, leading to potential confusion and makes it hard to research. Even Miike Takashi made a movie with the same title two years earlier. No wonder it is relatively unknown even though Tsutsumi is a well-established director.
Protagonist is the star psychologist and author Yuki, who decides to write a book about a woman called Kanna, equally famous as a murderer. Yuki kind of plays the role of a detective. As such, she is not as peculiar as they usually are. Still, her job pushes the investigation in the direction of psychology, while other areas like crime scene investigation and forensics are less focused.
The acting of Yuki is a little stiff in the beginning, when she and others talk like they are reading from the novel. She becomes more natural and convincing later when she gets into some tense situations.
When Yuki meets Kanna's lawyer Kasho, he warns her that even talking with Kanna can become dangerous. From this point, the story occasionally resembles the movie The Silence of the Lambs (1991).
Kanna is easily the strongest character. Smart, charismatic, and unhinged. Reasonable, but at the same time terrifying. She is very original, with a labyrinthine way of thinking. I don't remember anyone similar. She is actually not on the screen much, so maybe the rarity of her appearances makes them even more impactful.
With a setup like this, it is no surprise that the story goes into dark and sensitive topics of the kind that directors like Sono Shion like to explore. But Tsutsumi is a careful director who avoids controversy by tiptoeing around it with symbolism.
First Love almost has two plots, one that actually happens, and a shadow plot consisting of worse things that could have happened. This makes it less edgy, but draws less attention, and creates fewer shocking scenes to put in trailers. Absolutely don't watch the trailer by the way, because it spoils the entire plot.
The drama hides that it is basically a mystery. Tsutsumi is experienced in that genre, and it shows in how tight everything is, with virtually no plot holes or loose threads, and nearly everything is connected with something else. The mystery in his earlier movie 12 Suicidal Teens is theoretically solvable by the watcher, but so complicated that it is impossible in practice. First Love is much simpler, and almost appears to made for the watcher to figure out. If you want to take up his challenge, I recommend to watch about half of the movie, up to after Yuki's encounter with Yuji, and rewatch it from the beginning to snag clues you might have missed.
Visually it looks pretty and clean in a low-profile way. It seems that they try to use colours, light effects and reflections sometimes to symbolize various things. There is also a piano background song that I like.
Compared to The Silence of the Lambs, it is a bit lame, but if all you want is a nice puzzle mystery with dark undertones, First Love is near perfection.