This fic drops a semi-AU/future Shirou Emiya into the world of Sekirei where he proceeds to flip off the harem romcom genre....while still building a harem. Though, to be fair, the setting lends itself to harems even more than most anime romcom series. This Shirou Emiya is a bit more gruzzled and experienced, having spent years working as an Enforcer for the Tower. Between his experience there and his magecraft, fights with sekirei are very feasible, though he still struggles when facing some of the stronger ones. However, In Flight makes up for this by introducing conflict in ways that aren't pure combat. Primarily, it's in the form of Shirou getting used to his 'Flock'. Between breaking things off with Rin and Saber and struggling to acclimate to what Sekirei consider normal, the relationship between Shirou and his Sekirei slowly develops over the course of the fic. It's balanced pretty well with bumps and obstacles, lighthearted fun, heartwarming moments, and serious moments. Conflict also comes in other interpersonal relationships and also in the mystery of Sekireis, the tournament, and what the end goal is. The pacing and reveal of these is done well. All in all it's an enjoyable fic and I definitely recommend it. The fic ties together the two settings fairly interestingly, finding a comfortable middle ground between the two.
Much like gabriel blessing's other famous story, The Hill of Swords, In Flight drops our protagonist into a harem comedy series and makes it more serious. In Flight goes further in some ways, exploring the world of Sekirei, and making the implications of everything that's going on feel real. As an extremely long story, it goes through a good portion of the original series, and large swathes of original portions as well. Somewhat controversial, it can go surprisingly deep into the lore of Fate/stay night, and sometimes stumbles as a result. Many say, the characterization of certain Fate characters like Saber and Rin, who show up very late into the story, just don't fit. I think, the quality of the writing goes past such things, though people may disagree with me. Surprisingly epic, this long story goes through a lot of battles, a lot of living in between the battles, building relationships, and coming to terms with Shirou's past. It's a stunning story if you give it the chance, rough at it's edges, but full of feeling. I highly recommend it.