Mr. Hasegawa is the father of Shingo Hasegawa, and a firm believer that school work is much more important then things like fishing or hobbies. Due to this he tries to discourage Shingo from fishing and has an uneasy relationship with him at first.
When first met, Mr. Hasegawa gave a off cold vibes and bluntly expressed his feelings about fishing when Doremi's father attempted to talk with him. He has no problem expressing negative feelings about fishing, even going as far as to find Shingo's failure amusing since he figured he was bound to give up.
This could imply that he himself has been in this situation, though it isn't outright stated...
Once he finally realizes how much fishing meant to Shingo, Mr. Hasegawa began to open up and even helped him to catch a fish. In which showed him smiling and happy, until he was caught and he instead quieted down and blushed. Which implies he's actually a nice guy deep down.
Like most adults in the series he seems to like drinking as well and is shown to be enjoying himself with Doremi's father later on.
Mr. Hasegawa shares his sons tanned skin and dark hair and eyes. He is about the same height as Doremi's dad and wears baggy clothing consisting of a blue jacket over a white shirt and dark orange-brown pants.