hakuro (tensura), tensei shitara slime datta ken, artist request, official art, second-party source, 1boy, beard, facial hair, frown, full body, green socks, grey hair, holding, holding behind back, holding sword, holding sword behind back, holding weapon, holding weapon behind back, horns, japanese clothes, long beard, long hair, looking at viewer, male focus, old, old man, oni, pants, sandals, scabbard, serious, sheath, sheathed, simple background, socks, solo, standing, sword, transparent background, weapon, white hair, white horns, white pants, wrinkled skin