Much of the series, including this late-stage chapter, focuses on the psychological game between Tsukushi and his sisters. As the title suggests, the "mystery" is often a vehicle for the sisters to "expose" their true, often eccentric or affectionate, feelings toward their brother.
Some readers found the specific art style less "eye-pleasing" than the author's previous works, though it suits the "thinly veiled" suspense of the plot.
You can read the full series officially on platforms like Tonari no Young Jump .