First off, I just started reading this particular story because of Megumi. Of course, I am familiar with the Quintuplets, but I am not a fan of rom-coms. However, this is very well executed, the premise of Megumi someone who is traumatized and depressed, helping five different girls. The themes are pretty clear. obviously romance, family, and fear/anxiety. That's my synopsis or summary.
Some minor criticism from me, it's pretty noticeable that the lack of a large cast of characters is harmful. Because as soon as a scene involving the siblings starts or ends, it's easy to tell what is going to happen. Though you gave them more depth. Also, the aspect of JJK is very small so far and currently not relevant, considering the circumstances. However, I do hope it will be involved more in the future.
What I think is very well executed, is the drama.
It is rather easy to get immersed in. That's mostly because of the character interactions and dialogues. Everyone acts in a way that fits their character (else it would be probably harder to integrate Bumgumi), which makes the character arcs more compelling and understandable.
Another strong quality is the length and release of the chapters. Until now, new chapters come after 1 or 2 days, and as already said they are pretty long (I estimate ~2000 words per chapter, take it with a grain of salt, tho). The overall writing is very satisfying, not the usual forced sophisticated style or over-descriptions and straight to the point, but not necessarily dumbed down. It's pretty familiar and approachable.
I would like to see in which other directions the author can go after this fanfiction and am still very thrilled for more.
