Tasogare Otome x Amnesia, Hwaja Recommendations
If you like the combination of mystery and romance, this will scratch the same itch. I personally found the quantity of romance in Dusk Maiden to be more than Hwaja, but the maturity of content in Hwaja is definitely higher.
Hwaja tells of an evolving storyline with depth of the characters, while Dusk Maiden mostly consists of the present day, past flashbacks and evolution of the girl MC during the interim period.
Both stories are very touching, and dark.
If you want a darker more mature storyline, pick Hwaja
If you want more romance, pick Dusk Maiden
if you like one you'll be sure to like the other.