The Common Sergeant (Athyma perius) looks very similar to the Common Sailor (Neptis hylas).
The major difference between the two is the white strip found on the leading edge of the forewing.
On the Common Sergeant that white band is a single long dash with three dots.
The Common Sailor, on the other hand, has a longer dash line and a single dot.

Ben Tre area, Mekong Delta, Vietnam, 22 December 2023