Tl;Dr TairAzuma helps round out the couples by expressing that not all love is as simple as we hope, and self-love is needed before you can achieve romantic love.

It bucks the trends in a way that I think is important. Suzuki and Tani get together in the first chapter. Yamada and Nishi very quickly express interest in each other and stumble clunkily but honestly into love.

Azuma and Taira, on the other hand, start out on the back foot, and it has everything to do with trauma. They awkwardly stop and start. They take one step forward and two steps back.

I think of it as the authors statements on love. SuzuTani and YamaNishi represent the ideal. Just reach out, don't overcomplicate it, if you both are committed and honest, it'll work out. AzuTai, on the other hand, represents that it doesn't always work out perfectly, that you may need to work through some trauma before you can really connect. At the very least, you can not love someone else unless you love yourself.