Kingdom Hearts is a story-driven game that includes tough bosses that must be defeated to move on to the next part of the story. However, the game consists of secret bosses that don't have to be beaten to get to the next stage of the story but help players earn power-ups and new abilities that will help them later on.

RELATED: 10 Best RPGs With The Least GrindingSome of these secret bosses are easy to defeat and only take a few minutes to move past, but others are just as difficult to beat as the main bosses. By defeating the most challenging secret bosses, players can make it easier to defeat main bosses later in the game.

10 Ice Titan

Ice Titan From Kingdom Hearts roars

Ice Titan is an imposing boss, but with only one way to take him down, he is one of the fastest secret bosses to take down. Ice shards are Ice Titan's best attack and most significant weakness. The shards are the only way to take down Ice Titan.

His fighting pattern comes in three phases, so the faster players learn the pattern, the easier he is to defeat. As the fight continues, Ice Titan gets more aggressive and moves around more. Attacking early on is the best way to defeat this boss in Kingdom Hearts.

9 Kurt Zisa

Kingdom Hearts Kurt Zisa in the air

Kurt Zisa appears in Kingdom Hearts 1.5 as a secret boss Sora and his friends can face off with to earn more EXP and level up. Kurt is quick and hard to attack sometimes, but his body isn't the target. With the orbs he uses as the primary target, aiming and launching attacks is easier.

Items are essential when facing off with Kurt Zisa. The more things a player has, the better, as long as they know how and when to use them. Kurt has obvious moments of vulnerability that players can quickly capitalize on.

8 Phantom

Phantom comes out of the clock towards Sora

Phantom looks like a villain from other Disney games, like Disney Dreamlight Valley. He uses curses and a power called Doom to eliminate characters one at a time until only one player is standing. This makes it hard to keep a constant strategy of attack.

Phantom is limited as he can only carry one orb attack at a time. This gives players time to prepare for the next attack and find the weaknesses in Phantom's attacks. No orb is undefeatable, so with time, players can quickly line up their attacks to defeat Phantom.

7 The Unknown

Sora faces Unknown in Kingdom Hearts

The Unknown comes in Kingdom Hearts The Final Mix and is one of the most challenging secret bosses to beat if players haven't explored other Kingdom Hearts games. The Unknown isn't listed in the journal, so players don't know how to prepare.

RELATED: Which Kingdom Hearts Character Are You, Based On Your Zodiac Sign?

However, once in the fight, it is easy to determine when and how he will attack. Players who help Sora avoid lighting and force fields can time their attacks to take down this secret boss. Other characters like Donald and Goofy can help defeat Unknown, making him faster to defeat.

6 Vexen

Vexen Kingdom Hearts Smiles

Boss fights are meant to test players' skills, but Vexen is a tricky boss who can also learn these skills with a quick scan of a player. This makes Vexen hard to beat, as there is no hiding the abilities Sora has learned in Kingdom Hearts II.

Vexen has a shield that is hard to break, but once it is damaged, taking his health down is much easier than other bosses. For players who have reached a high level with Sora, this boss battle should be over quickly, but for those who haven't defeated other secret bosses or are of a lower level, this battle will take a reasonable amount of time.

5 Laexeus

Laexeus prepared to fight in Kingdom Hearts 2

Laexeus is one of the few villains in Kingdom Hearts II that gets stronger the longer he fights. With each blow, his strength can increase unless players know how to counter the attacks properly. Once players get used to Laexeus's fighting style, they can block more quickly.

However, this may take a few tries, and players may find themselves defeated before fully grasping Laexeus's powers. The faster players notice Laexeus's vulnerable moments, the faster they can move on from this secret boss.

4 Sephiroth

Sephiroth from Kingdom Hearts 2 with swords drawn

Sephiroth is the first and only secret boss in Kingdom Hearts, appearing after the first game's main story is complete. Sephiroth starts one of the hardest fights in JRPG games, but also the Kingdom Hearts franchise. Timing is everything when fighting Sephiroth, as the final spell he casts can deliver the final blow to Sora if players don't stop him from releasing the magic.

This boss moves fast with each version of his attacks, so being quick will help make this battle short. Sephiroth may take more than one try to beat, as he uses so many magical abilities to defeat his opponents.

3 Dark Inferno

Dark Inferno standing in a desert with swords drawn

Dark Inferno is a difficult secret boss because he is strong and takes effort to find. He appears after players have finished the story in Kingdom Hearts III, but if players have not fully leveled Sora up or created the most powerful keyblade, it will be impossible for Dark Inferno to be defeated.

RELATED: 10 Disney Worlds Kingdom Hearts 4 Should Avoid

Dark Inferno doesn't use much strength to take out Sora, so players must be ready to dodge and attack as quickly as possible. The battle takes place in three parts, so knowing what items to use when is essential to winning.

2 Data XIII

Data XIII posing together

Defeating Data XIII has its benefits, as it upgrades Sora's crown, but it is one of the more difficult secret bosses. Data XIII is a group of villains rather than one, so players must study all the members' attacks and be prepared to move from one foe to the next.

Players who have played through Kingdom Hearts II more than once will fair better against these secret bosses, as they are a more powerful version of the Org XIII member they fight at other points in the game. Their attacks are almost the same as the original characters but stronger and faster.

1 Lingering Will

Lingering Will in Kingdom Hearts II

Lingering Will can be found after the unforgettable end of Kingdom Hearts II. As the most demanding secret boss Lingering Will test players' ability to react quickly and the skills they have learned throughout the game.

If players aren't at the highest level they can reach by the time the initial story mode is done, they won't be able to beat this boss. Unlike other bosses, Lingering Will doesn't rely on one attack style. He changes his move set once he drops health levels, so players must be ready to adapt to the new moves quickly.

NEXT: 10 Disney Worlds Kingdom Hearts 4 Needs Most