Was that Ken's older brother?
In the movie The Proffessors son Ken is talking to this college age guy who is also seen with the girl and is seen hallucinating in the night club.
He forms the rock & roll party on Mt. Fuji and when Hedorah attacks is the first to be Sludged to death with toxic mud spit.
I don't think he was Ken's older brother as he referred to the Prof. as 'Professor'. My guess is he was a lab assistant or maybe the girl was Ken's older sister and he was the boyfriend.