I’ve posted about this before, but the story roughly goes along:
Visuals: The manga itself had a similar art style to Tobi Washio’s “The Panther’s Pet”
About the characters: Black haired bottom, blonde top with dark roots (not too sure about this one)
The bottom is a researcher/scientist/top student (i really cant remember) from a really well known college and has been working in the same lab for a while. The top (I think he was blonde? From what I remember) owns the lab that the bottom works at because his grandpa, who was the bottom’s professor/boss (again, not sure if this is accurate.) plays a huge role in the company/college that they worked at.

okay so the top was american and stayed either in japan? or america for a bit and he met this black haired guy near a beach (i cant even remember anymore) it was a bl manga though