I will suggest Initiative, Ninjutsu, Taijutsu, Defense, Resistance, Life as the main ones. If the character is more Taijutsu based you can ditch Ninjutsu and same for the other. Also Initiative is a must only on position 1, but if you have a barrier ninja you need Initiative on everyone.

Then I will suggest Ice (control) for CC ninjas along with the Gourd treasure tool.

Critical an Injury you get from the Rope treasure tool so if you want bonus damage you should go for them and enhance that, rather than Nin and Tai pene.

Reason why Nin and Tai pene are bad is that they don't add up to damage if you have more than the opponents Damage Reduction, and you basically have more than that by default since they don't go for Sand runes, this is why I also suggest Sand for supports.

Also I would take Explosive(Critical) over Injury, it doesn't matter how hard you critical if you don't get the critical in the first place.