6* is the highest grade a character can attain which sets his/her level cap to 50. This can be further increased up to LV60 by feeding other 6* characters to the character you want to limit break. Each limit break only increases the level cap by 2 levels so you’ll have to go through 5 limit breaks for a character to reach LV60. After limit breaking, you also need to max out the character’s level again before you can break the level cap once again. Here are the necessary 6* fodder characters needed per level:
50-52: 6* x1
52-54: 6* x1
54-56: 6* x2
56-58: 6* x2
58-60: 6* x3
Limit break doesn’t only increase the character’s stats but also allows them to unlock a new talent every 2 levels. At LV60, you’ll be able to unlock the character’s second passive skill. These passive Skills are very powerful and unique to the character, making them even more potent and effective.
There’s no limitation about what heroes that can be used as fodder in limit breaks as long as it’s 6*. As such, be careful not to accidentally feed 6* SSR heroes, advent heroes, and enhancemons. SSR heroes should be used for enhancing their original’s Skills while advent heroes and enhancemons should be exclusively used only for enhancing a hero’s stats. You should be primarily using evolvemons and sometimes unwanted Rs and SR characters when limit breaking.