Post a character who sometimes uses a weapon and sometimes doesn't.

How 'bout almost all characters from soul eater?

They use their weapon almost always, but still there are times they fight alone........

Well, Kenichi is studying a wide variety of martial arts, some which use, and others which don't use weapons.

Janemba

Accelerator from To aru majutsu no index

~Sometimes he'll kill you with a gun, sometimes he'll just rip you apart with a touch of a hand XD

Sebastian (Black Butler)

Toriko uses weapons a few times but the MAJORITY of the time he uses his very OWN body as a weapon including his feet. So Toriko is essentially the embodiment of a living weapon

FMA they sometime use weapons and some dont