If you reinforce levels of weapon card and skill card each to the max stage, 

you can fuse them.

This fusing is possible only with a max-level card, 

and by fusing different cards of the same level, you can get random one upper-level-rank card.

But if you combine identical cards on the same level, you can gain one upper-rank identical card. 

While you proceed with fusion, equipped option cards will disappear so keep that in your mind. 

Kinds of cards that are possible to fuse- Weapon cards, Skill cards and Option cards. 

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