Thread:Ragnarok6354/@comment-25856250-20150227142728/@comment-11148831-20150228080609

Well, yes. But it is only 100% guaranteed to level up when you use same skill, same level.

Currently the only known way of doing so with 100% success rate is to have the card you want to increase the skill level of train with another card with the exact same skill at the same or higher skill level. For example, if you have a card with Perfect Charm at level 2, in order to increase the skill to level 3 with 100% certainty, you must have feed it another card that also has Perfect Charm at level 2 (or higher). If you feed it a card with a lower level skill of the same type, there is a chance that the skill level will not increase. Training with different skills will have no effect on level at all.