High School Debut does not lack reviews, but well, I'll write another one, because I feel like - even if the score on MAL is quite high - this manga is unappreciated.
Warning: this is gonna be loooooong!

I wasn't expecting much - plot sounded kinda cheeky and very typical-shoujo-like. But! How could it be typical, if the author is Kazune Kawahara, who is also after stories of (the most unique, original, too cute to handle) Ore Monogatari!! and (wonderful, warm, touching) Tomodachi no Hanashi? But I'm glad that I didn't realize who she is, thus I had no high expectations...
What a sweet surprise it was!

Story - 9 - GREAT
At first, story seems cliche. Haruna was busy with sports in middle school, and since she always give her best at whatever she does, she didn't have any time for love life. However, it's not like she hasn't thought about it! She's been reading loads of shoujo mangas and magazines, and she's promised to herself that she will find a boyfriend in high-school.
The problem is... Haruna doesn't know how to attract boys, what's more - she is driving them away with her weird, overdone outfits. Her friend gives her an idea: why won't she look for a coach? It worked well with softball, why not love&beauty?
Good thing that there is someone ideal for such job - Yoh Komiyama, handsome and popular guy that Haruna earlier met! Although he claims that he hates girls, eventually he agrees to be Haruna's coach with one condition - she can't fall in love with him.
That's how their story started.
It's pretty predictable what will happen next, right? Well, hell yes,

!!!OBVIOUS SPOILER!!!

she falls for him, but not instantly. She gets to know him, and he gets to know her. Their bond is something that forms very naturally, you don't feel like it's just mangaka's caprice. Relationship between those two progresses through whole manga, and I don't mean that it's slow, but that their affection grows and becomes more mature, just like it should be. Sometimes in shoujo characters just get stupider and more childish with time, but not here.

The story is simply about their relationship. It's nothing really big, so why I scored it so high? Well, because it's nothing really big. There are none imposed dramas. There are many moments of struggle, sure, but characters don't act like their lives are going to end because of it, they just solve their problems, and it's so great to watch them do it!
Also, you won't have any fireworks festival here, neither beach day nor camping. The story is simple, but yet not cliche.

Why I didn't give it a 10? Because in this manga you will meet plenty of interesting characters, and you'll only know stories of few. I want moar! Also, there are some ideas that could be expanded. Not need, but could.

Art - 9 - GREAT
It's simple, but pretty. I like that heroine is muscular and not slender - she is strong and good at sports, and she looks like it. Besides, her smile will brighten your day.
What's also great - every character is different, with their own unique features, like shape of eyes and stuff, they don't only differ in hair colours (yes, I'm refering to most of shoujo bishes).
I'm taking one point off because I can't really say anything about backgrounds. They were. That's all.

Character - 10 - OUTSTANDING
Yes, they deserve a ten!
Haruna may seem like your typical cheerful naive girl, but she is a ray of sunshine. How often you hear from a girl "I'll protect you" towards a guy? She's all about protecting Yoh! She treasures him so much, that it will melt your heart.
WARNING: watch out if you easily get secondhand embarrassment (like me), because Haruna is incredibly straight-forward, she doesn't beat around the bush at all. So be ready.
Despite her joyful, silly behaviour, she really is sensible, strong and brave. If she does wrongly, she notices it and improves.

Speaking of improving - Yoh! Your gloomy tsundere boy. The character development is strong with this one! He changes, but somehow he's always himself. He's awfully blunt, but also very kind. He has his problems and scars, but he isn't unable to move on. He's not the first to talk about how he feels, but when he does... he makes you melt, just like Haruna. Don't judge him by his looks and first impression, there sooo much more in him.

Their friends are all very interesting, but I think that Asaoka and Assa are most intriguing. Assa, Yoh's sister, claims that she has bad personality - well, she isn't wrong. She always tease Haruna, act mean very often, is narcissistic and not sincere... but she is likeable, somehow. There is a lot of complexity in Assa, and you should form your own view about her.
And Asaoka? I'm still not sure what's on his mind. He is kinda manipulative, smart, intelligent, cunning, but he cares about his friends. You can say that Assa teases Haruna, and Asaoka teases Yoh...

Enjoyment - 10 - OUTSTANDING
What can I say? It was really a sweet surprise.
The characters haven't disappointed me single time. I enjoyed every one of Haruna's and Yoh's interactions, their progress and changes. It was so nice to watch them surmount obstacles. Gags (and Haruna... mostly Haruna) made me laugh to tears, and the story made THINGS to my heart.

Overall - 10 - OF COURSE!
If you are tired of cliches, read this manga. If you are tired of stupid dramas, read it. If you crave some solid character development and healthy relationship between characters, read it. If you want to have THINGS done to you heart (what even), I highly recommend this manga.
If a simple shoujo manga makes one go spend their evening on wirting ridicously long review, you know it's good.