How can I complete S rank missions?

SOLUTION 1:

Hmm, Try using Yamato as your playable Character, and try to complete the SS Mission "Sound of the Bell".

Just remember to equip the following Scrolls to everyone:

Book of Attacks Lv. 4
Null Complete Seal Lv. 4
Null Paralysis Lv. 4
Book of Health Lv. 4
Book of Chakra Lv. 4
Hidden Dream Tome Lv. 4
Amagiri Secrets Lv. 4
Hirasaka Secrets Lv. 4

Try equipping Scrolls that Null Paralysis, Complete Sealing, and Chaos.

When the Mission Starts, use Water Style: Ripping Torrent on the enemies, and try blowing them off the Cliff to defeat them quickly. Then with the enemies that don't stagger, use Great Paper Bomb, and/or Paper Bomb (Burst), as well as Kunai, and Shurikens(NOTE: it can be any type of Kunai or Shuriken)

NOTE: if you use Paper Bombs/Shurikens/Kunai, Don't Go crazy with them, because you only have a limited Supply of them. Unless you equip the "Ninja Tools Scroll".

Also, don't forget to use Kizuna Finishes on them to beat them quickly as well.

SOLUTION 2:

Also, Here's a list of Characters to use, and What to equip to them:

NEJI: Byakugan, 8 Trigrams Palm Rotation, Great Paper Bomb, Three-Way Shuriken
NARUTO: Wind Style: Rasen Shuriken, Nine-Tails Power, Great Paper Bomb, Three-Way Shuriken
SAKURA: Medical Ninjutsu, Regeneration Tag, Heaven Kick if Pain, Three-Way Kunai
SASUKE: Fire Ball Jutsu, Great Paper Bomb, Three-Way Shuriken, Paper Bomb(Burst)

NOTE: If 1 Recovery Type Character isn't enough, then bring 2 or more.

But NEJI is your Best choice to play as. So, when using NEJI, activate "Byakugan", then try hitting the enemy with the 8 Trigrams: Mountain Break Attack combo(Circle x4, Triangle) as well as the 8 Trigrams Palm Rotation. But try blowing the enemies off Cliffs to finish them, because they're SUPER HARD to kill with combos, but Paper Bombs deal lots of Damage as well.

It took me a few tries, but I beat that Free Mission using NEJI. Had I known that YAMATO was a better Choice, I would have chosen him., But I hope this helps even with only 490 Attack, 600 Health, 500 Chakra, and 100 Defense.

I think you going to full your kizuna points. To get that use assist , heal or the kizuna finish to get kizuna points