Yes, ninjas were a real thing. No, they didn't habitually wear all-black pajamas and carry straight-bladed katanas - not until the 1980s, anyway. It's taken me years to decide it was okay to add a couple of decent quality "ninjato" to this website, but since I've started a Film and Fantasy section where I can cross-index them to the more traditional Japanese swords, here are a couple of select examples.
This "Practical Shinobi Ninja-to" is made by Hanwei, who are known for their Japanese (and European!) sword-crafting. The hand forged blade is differentially clay-tempered 1566 high carbon steel, sharp and functional. The fittings are blackened/antiqued iron, with synthetic same' and a durable synthetic leather wrap tsuka-ito. The flat-black saya has a cotton sagayo and an intricate kojiri.
(oh, by the way - "shinobi" may specifically refer to male ninja, but kunoichi can enjoy these well-made swords too.
length: 34 1/2"
blade: 22 3/4"
blade width: 1 1/8"
tsuka: 10 1/4"
balance point: 4 1/2"
weight: 1 lb 14 oz