Unfortunately it’s highly unlikely… firstly, Yamamori-sensei doesn’t want an anime adaptation for her manga. I forget where I read it, baidu thread perhaps? But I wouldn’t blame her, manga-turned-anime series are often massacred. Secondly, this one surprises me, but HNR doesn’t sell as much as other popular shoujo series. Even Mairunovich (most poisonous trashy shoujo to ever exist in my opinion and I’m vocal about my dislike because of the nasty and shallow messages it sends to readers) sells better than HNR. Tumblr’s Hirunaka fandom is pretty large for a shoujo fandom but Tumblr’s fandom is mostly English and relies on illegal scanlations which don’t count as sold copies.
Lastly, the manga series is to conclude by November 5th of this year. An anime adaptation would take time and by then the fandom will have faded. Series are generally animated while the manga’s still ongoing so interest doesn’t fade. I’m heartbroken about such a lovely series concluding but I’m happy nothing’s going to be uselessly dragged on, and I’m happy to have just the manga without any disappointment about an anime adaptation.
Plus -this isn’t an actual reason but just my own thoughts- most anime that’s based on manga only adapts part of the manga, not the whole thing. The first half of Hirunaka no Ryuusei is very Shizume-heavy, and the majority of HNR’s fanbase supports the Mazume ship. I suppose the adaptation would only include the first half at most, thus leaving most if the fanbase unsatisfied. For such a divided fanbase, it’d seem a little unfair for the Mazume fans anyway. Just my thoughts 8^) I think we’d all be better off without an anime honestly.