In shamisen bunkafu tablature, quarter notes have no underline. 8th notes have a single underline and 16th notes have two. So, that measure is comprised of three 8th notes and two 16th notes. If you think of the underlines as the tails on notes in Western notation, it makes more sense.
Half notes aren’t as common in notation, but if you do come across one, it’s represented by a quarter note followed by a dash.