Quite good but...
The idea of this game is excellent, but it could have executed better. Game is quite similar to some trading card games like Yu-gi-oh. Too bad that the game has some major flaws which reduce its overall rating. Let's see...
Basic idea is to combine right cards with correct timing. Unfortunately card selection is WAY too huge, making chances of drawing tha cards you need slim to none. That's not good, especially when most of the card are just better versions of the some card. ( Gain 1 health, 2 healths, 3 healths etc.) Because of this the game is based more on luck than strategy. It's especially frustrating when you draw weak healing cards like "cold sake" while opponent draws powerful damage cards like "critical hit".
Also, some of the cards are way too powerful. For example, if opponent regenerates 2 HP every turn it's nearly impossible to win. The only way to counter regeneration is "vorpal blade" and with 110 cards in deck it is NOT likely to get one when you need it. Same goes for bleeding. 1 HP each turn doesn't sound much, but when it lasts for 40 turns with no cure you simply bleed to death.
It IS still possible to pull off some great card combos. For example when opponent uses poison you counter with "Inexperience" and "Dishonorable blow". Or when you have lots of hazumi you can use "Defencive stance" to get your hazumi in defence and then use "versatility" to switch your offence and defence so that it will not revert.
The game has some bugs that should be fixed.
1. If opponent plays "Strategy" or "Tactics" he will not discard. Instead, you don't get new card when your next turn starts.
2. Tackle has no effect. Opponent get his defence score back before you have a chance to attack him.
3. If you have 5 or less cards in your hand and press empty cards slot you will just skip your turn.
Other negative things:
1. Training is meaningless
2. Bonuses from tournament are for one-time use.
3. If you lose a trial you immediately lose a belt rank.
4. Because opponent has 5 HP more at each rank of belt trial it's almost impossible to win at highest ranks. I had gray belt at best.
5. It seems like opponent cheats. No matter what player does opponent has counter.
Game would improve if bugs were fixed and some useless cards were removed. Or you could build your own deck. It would also make game more balanced by limiting the number of powerful cards.