First off, Rei is an ML who is far from your dreamy "I can fix him" kind of trouble. Despite having a carefree charm, Rei can also be straight up unhinge. He is the titular "Mars" of the story, as in the god of war. Rei will straight up crush anyone who goes against him, and I mean ANYONE, without remorse. His main passion is motorcycle racing and it's a driving force for many of his decisions in life. Kira at first glance feels like your typical timid girl MC. Yet she has this inner strength that makes you root for her. She does cry a lot and can be very naive, but the cause of her emotionally stunted state is slowly revealed throughout the story. Both leads face many drama and trauma, but the story doesn't justify their actions. They can mess up, just as you do when you're young.
Still, Mars has one of the most natural chemistries between the leads. They have this pure empathy and care for each other that goes beyond the "doki doki". You can feel they genuinely enjoy each other's company and just feel comfortable together. Their dynamic is less "I can fix you" and more "You are not alone in this sh*tstorm of problems". The amount of trauma dump can feel quite melodramatic, but their trials and tribulations is what makes the character development throughout the story so fulfilling.
The art itself is some of the best I've seen in Shoujo. The style is realistic and vivid, but the panel work really drives home the emotional state of each character. That, accompanied by the dialogue that cuts deep, just make reading so investing.
Overall, it's a great character study and a mature love story. Despite going melodramatic, the characters felt raw and real. I would not recommend reading if you don't like morally gray characters or want to avoid triggering subjects. Honestly don't understand how this manga is considered Shoujo and not Seinen based on the mature themes and how dark it went. I'm glad I didn't read it as a kid when it was popular, the amount of angst would've scarred me and I would not have appreciate the nuances. Reading Mars now, I can't help, but feel touched by the journey.
Ps. The racing are so well drawn! The racing fan in me feel so hype every time.
