In Ultimate Ninja Blazing, 6 star is the highest rarity and those characters are the most powerful. However, 4 or 5 star characters also works well. This page shows the most useful characters less than 6 star based on their stats, moves and field skills. This list is in no particular order.
Haku has the new limit break feature available to him. He is very similar to the limit break Rock Lee but not quite as good. He is Heart type whilst Rock Lee is Body so will hae uses in other missions. For details of Haku, .
This new Hinata over takes the old one in a few way as she is now able to heal with her Field skill. She also has 3 perfect dodges for 3 turns so is great for avoiding bosses Ninjutsu. She also has good stats for a 5*.
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Also, Tayuya has an AOE ninjutsu-sealing jutsu which has saved my life many times when facing multiple foes trying to do jutsu at the same time. Definitely overrides Hinata.