The storyline revolves around Jin Kazama and his devil form, Devil Jin. It is similar to the Tekken Force modes in Tekken 3 and 4, but unlike them, Devil Within does not allow the player to select their desired character and it has a story line to accompany the fighting, which the "Tekken Force" modes lacked.
It is not known if Devil Within is canon or not, but it's stated in Jin's prologue that he sets out on a journey with destiny as his only guide to end the evil that was plaguing him. It can be concluded that Jin's journey was the Devil Within story line. Jin is also the only character in Tekken 5 who's prologue didn't state that he entered the King of Iron Fist Tournament 5.
- Stage 1 boss - Modified Gun Jack
- Stage 2 boss - Clone-Heihachi
- Stage 3 boss - True Ogre
- Stage 4 boss - Soul Sphere
- Stage 5 boss - Monstrous Ogre
Jin has heard that his mother, Jun Kazama, may be alive. However, he does not find her anywhere. Instead, Jin confronts his worst nightmare, True Ogre, again. True Ogre will reveal another form after being defeated for the second time, Monstrous Ogre (this Ogre has a slightly different skin tone, it is more yellow then green and is much bigger). Jin must defeat this form, as well.
- After beating Devil Within under medium difficulty and collecting all the Evil Symbols, you can play as Devil Jin through the entire game by holding down L2, SELECT and R3 while selecting a stage or starting a new game. The Devil bar will become your laser bar. The downside of this code is that enemies die faster, lowering your chance at getting a high combo.
- Devil Jin's appearance is different in this game, his eyes and his body glow red.
- Jin, as his normal self, fights using the Advanced Mishima Karate fighting style.
- Jin transforms into Devil Jin differently. He leans forward while transformed already, then leans backward and lightning surrounds him.
- The theme of Stage 1 and during boss fights is a remix of Jin's theme in Tekken 3.
- Another way of unlocking the Cathedral and Final Stages are to unlock Devil Jin without finishing Devil Within which is done by finishing Time Attack with Jin or doing 200 arcade battles.
- Jin's lower body design is Devil Jin's lower body design (whole red flames on the right leg wearing two shoes with the right shoe being the same color as the flames).