Uppercases slot defines.

code/modules/ninja/energy_katana.dm

@@ -13,7 +13,7 @@
 	hitsound = 'sound/weapons/bladeslice.ogg'
 	attack_verb = list("attacked", "slashed", "stabbed", "sliced", "torn", "ripped", "diced", "cut")
 	block_chance = 50
-	slot_flags = SLOT_BELT
+	slot_flags = ITEM_SLOT_BELT
 	sharpness = IS_SHARP
 	max_integrity = 200
 	resistance_flags = LAVA_PROOF | FIRE_PROOF | ACID_PROOF
@@ -79,7 +79,7 @@
 
 	if(user.put_in_hands(src))
 		msg = "Your Energy Katana teleports into your hand!"
-	else if(user.equip_to_slot_if_possible(src, slot_belt, 0, 1, 1))
+	else if(user.equip_to_slot_if_possible(src, SLOT_BELT, 0, 1, 1))
 		msg = "Your Energy Katana teleports back to you, sheathing itself as it does so!</span>"
 	else
 		msg = "Your Energy Katana teleports to your location!"

code/modules/ninja/outfit.dm

@@ -11,7 +11,7 @@
 	back = /obj/item/tank/jetpack/carbondioxide
 	l_pocket = /obj/item/grenade/plastic/x4
 	r_pocket = /obj/item/tank/internals/emergency_oxygen
-	internals_slot = slot_r_store
+	internals_slot = SLOT_R_STORE
 	belt = /obj/item/energy_katana
 	implants = list(/obj/item/implant/explosive)