I know every manga can have a similar character designs but Lynn Okamoto may have been one of the biggest offenders since it's hard to tell if it was supposed to be intentional or he was just lazy.
In Elfen Lied, Nana has a identical character design to that of Kurama's wife and considering her relationship with him, I always wonder if that happens to play a role on why he cared about her. But then you have #28 and Nozomi...also when comparing Okamoto's other works, in Nononono, the protagonist resembles Yuka. Then you have a genderflipped version in Ryouta in Kiwaguro.
Granted in Nononono, it was likely intentional considering you have a journalist and his assistant resembling Kurama and his assistant.
But then in Kiwaguro, without the color panels the only way to tell apart Hatsuna and Kazumi is that the former has her hair tied to one side, otherwise they'd be impossible to tell apart.
Could have at least put in more effort on Hatsuna's character design.