Story mode achievements are the easiest and quickest to get, it doesn't require you to finish side quest unless it's told to if they tell you to meet "information characters"

Genin Training Arc Complete
Completed the Genin Training Arc.

Overflowing with Innocence
Completed over 10% of the missions.

Chunin Exam Arc Complete
Completed the Chunin Exam Arc.

Leaf Destruction Arc Complete
Completed the Leaf Destruction Arc.

A Long Road Ahead
Completed over 20% of the missions.

The Search for Tsunade Arc Complete
Completed the Tsunade Search Arc.

You've Got Potential
Completed over 30% of the missions.

Chasing Sasuke Arc Complete
Completed the Chasing Sasuke Arc.

Hidden Leaf's New Hero
Completed over 50% of the missions.

Easy Achievements are those with higher percentage and definetely easy to obtain with less effort, it can be done either solo against the AI or against another player

Finish with an Ultimate Jutsu!
Finished an opponent with an Ultimate Jutsu.

Finish with Ninjutsu!
Finished an opponent with Ninjutsu.

Finish with a Full Power Ultimate Jutsu!
Finished an opponent with an Ultimate Jutsu with the Storm Gauge at MAX.

Finish while Awakened!
Finished an opponent while Awakened.

This is how a ninja fights!
Finished off an opponent from a wall.

Succeed with a Supportive Extra Hit!
Attacked an opponent with a Supportive Extra Hit.

For these achievements you must prepare ramen bowls with Teuchi at his restaurant buy Action Figures, Music Themes and Ultimate Jutsus to go get these ones
Note that making ramen and not fully buying products at free mode is not mandatory but the game will ask you to get least half of it if you want achievements

Ramen Lover
Created a new Ichiraku Ramen.

Newbie Figure Collector
Acquired a Figure.

Ultimate Jutsu Fan
Acquired an Ultimate Jutsu Movie.

Ramen Gourmand
Created 10 or more different Ichiraku Ramens.

Music Fan
Acquired a music file.

Order Representative
A new item was added to the shop.

Amateur Figure Collector
Acquired over 30% of all Figures.

Veteran Figure Collector
Acquired over 50% of all Figures.

Music Maniac
Acquired over 30% of all music files.

Music Master
Acquired over 50% of all music files.

Ultimate Jutsu Master
Acquired over 50% of all Ultimate Jutsu Movies.

Painful Achievements will take you an eternity to get because either the Steam Version Achievements are broken or the player didn't understood how to get them, so there are a now ways to achieve without any caused problem

Prevent an Extra Hit!
Prevented an opponent's Extra Hit.
(It's not hard IF you get enough reflexes and your teammates weren't used, it also can be done naturally)

Finish with a Throw!
Finished an opponent with a throw.
(Your enemy must be off guard/in a very close range with its life being at the edge of getting knocked out, with guard and hit button this can be done easily)

Interrupt an Ultimate Jutsu!
Interrupted an opponent's Ultimate Jutsu.
(Avoid by using substitution Jutsu or block)

Finish with an Ultimate Impact!
Finished an opponent with an Ultimate Impact.
(Like "Prevent an Extra Hit! Achievement" you have to hold "Hit" button and this will give a powerfull knock to your enemy and take a good quantity of its life, but your enemy must be at the edge of losing)

Ninjutsu Clash!
Won a Jutsu Clash.
(This one even with a low percentage there's an easy way to make it. You must select 2 identical characters (Pick Naruto for both players with Rasengan as Ninjutsu), the map won't be important, then both players must use Ninjutsu. NOTE THAT PLAYER 1 MUST WIN THE CLASH)

Finish with Support Ninjutsu!
Finished an opponent with Support Ninjutsu.
(Your support character must have a Ninjutsu selected)

Finish with a Ninja Tool!
Finished an opponent with an item.
(This one took me time to understand, some characters have specific tools, so I took anyone and used Paper Bomb tools (I advise this one). The enemy must be at the edge of its life

Finish with a Support Combo!
Finished an opponent with a Support Combo.
(This achievement is the one most people on the community have been struggling to get, therefore I found a way. Some people have been throwing the enemy with a combo and maxed gauge to finish the match with the support character. It took me loads of tries to understand this one. Pick any character but support must be Rock Lee with combo attack. The enemy's life must be calculated before finishing it. With the support character, your teammate must give the finishing blow (meaning all combos must be executed by it), then this achievement will appear

Finish with a Downed Strike!
Finished an opponent with an additional strike after downing them.
(Like "Finish with a Support Combo! Achievement" the enemie's life must be calculated but you won't need accuracy at all just patience. You can do this with a second player with a Handicap supperior and the second player being AFK. Once your enemy gets downed by any attack that put it down close to you, use the down strike attack to finish the match)

This one can be made during free mode and will take time (Since Naruto will only master the Rasengan after meeting with Jiraiya and training with him a The Search For Tsunade Arc) but they're not even hard to do, just patience

Ninjutsu 101
Acquired a Ninja Handbook.
(It'll appear in free mode when a green icon as a hidden box appears, any box can be)

Support Ninjutsu 101
Acquired a Support Ninjutsu Book.

Acrobatic Ninja
Performed six or more successful rope actions.
(This one is extremely easy and can be done in seconds. Find ropes and do a combo (the ropes can be seen once you're in game)

How to Use a Rasengan
Destroyed a door with a Rasengan.

Ninjutsu Master
Acquired 14 or more Ninja Handbooks.

Naruto Cannon Novice
Cleared 12 or more rings with one Naruto Cannon.
(You must eat good quantities of Ramen to increase your chackra to do Naruto's Canon Jutsu)

Support Ninjutsu Master
Acquired eight or more Support Ninjutsu Books.

Shuriken Pro
Destroyed five or more objects with one shuriken toss.
(There are two achievements and you can have both in one go. Go to the Item Store next to the flower shop and buy Shurikens until you have 10 (Pack of six is the last one and will cost a lot) and find at 10 or more flying scrolls hidden at the top of the building and activate the combo, the game will select the scrolls automatically and you'll obtain both achievements easily)

Shuriken Master
Destroyed 10 or more objects with one shuriken toss.

Naruto Cannon Pro
Cleared 24 or more rings with one Naruto Cannon.

Naruto Cannon Master
Cleared 42 or more rings with one Naruto Cannon.

After Approximately 30 hours (if things are done correctly) you can and will achieve the long waited achievement, this one only appears if you did 100% game completion

Perfect Storm Master
Unlocked all the achievements.