Looks like the Six Samurai have picked up some Ninja techniques in Spirit Warriors

DBSW-JP007 六武衆の影忍術 Rokubushuu no Kageninjutsu (Shadow Ninjutsu of the Six Samurai / Shadow Art of the Six Samurai)

Quick-Play Spell

You can only activate 1 card with this name once per turn.

(1) Send 1 monster you control to the Graveyard, then target 1 of your banished “Six Samurai” monsters; Special Summon it.

Note – the card is literally “Shadow ninjutsu” but due to how similar it is to the “Ninjitsu Art” cards, we’re listing it as “Shadow Art” for now to avoid confusion. We may revise this decision once the full set content is known.

Source