From experience I can say it's hard to write romance, it's also hard to write age gap romance between a 10 and 20 year old, and it's even harder to sell it to the audience.
But they did it, they accomplished it and the final result is the most wholesome and heartwarming romance ever animated by Japan.
The key to success is to make the characters believable and entertaining at the same time, our protagonist isn't over the top and the love interest naturally wasn't into the whole thing at the start, on the contrary even though the older girl was really shy and lovestruck like a pure maiden, the young one still had a hard time even trusting the cosplaymaker.
But like the human characters they are, there was character development, things didn't stay static, progress was made and the characters grew, both as a person and to each other. And the show left pretty clear they complement each other very well, one has terrible fashion sense and it's essentially useless at homechores while the other has big social anxiety issues, and they motivate each other to work on these flaws, depending more and more on each other while the show goes on, their dynamic getting better while at the same time growing together.
It was proven why the art direction and sound were 10/10 thanks to the final episode, but everything else was 10/10 thanks to our main couple.
There are all kinds of couples in media, couples with a strong bond that weren't shown how they got so close but still leave a big impression like Kanon x Koyori, couples that are pure concentrated sugar that depend on fluff more than on substance like Noa x Hinata, and couples that we see grow from nothing into something big with the biggest focus and evolution of their romantic feelings like Miyako x Hana.
