I suggest leaving his default a slot, he needs less atk to trigger Sagitate's effect, even with it i had difficulties triggering his weapon effect, if you really want a speed boost for him use speed ploy (4* Saias) in his c slot or SS slot.
CC is nice option on him if you need it, but i think you can lower his atk stat by runing fortress def in SS slot.
IMO he his better with the fortress skill, it gives him a lot of bulk and helps him to trigger the Sagittae's effect. He will work better with his base A slot + distant defence. That's potentially 45 def and res on the enemy phase.
But if you love him and have the fodder you can try it, but it seems it's a less efficient build for him.
CC is kinda meh on him because his player phase is so good. And running a fortress in his SS slot is a waste of potential because you give up so much for so little gain. His A skill default is gonna be best especially because you dont have an attack bane on him so tanking ranged becomes questionable as is. Just be careful you can apply his tome when taking a hit from Lynhardt.
With those ivs I'd say the better question is "what do I want in his B slot" because Chill Speed may be redundant. With so much speed (+5 on tome activation) you double everyone with 40 speed or lower. Some good ideas would be something like guard, vantage, links, a different chill. Avoid breakers and desperation as he won't need them. And you will not need QR at all. I suggest Guard because with -HP you get into that scary "i'm gonna die from your special alone" threshold of 35 and lower.
For C slot If you keep A skill I recommend Res ploy. Mine is +Res so it may work better but neutral should be fine for it as well.
For seal based on how combat works I will always recommend flashing blade. This allows him to KO quite a few armors and he generally can survive most DC hits they dish out back. I cant think of one that may work better except maybe DD3 if you really wanna tank ranged better than you already do.
Here's mine for reference and you can ask me any more questions you may have
RoyAhoy and I looked into Kliff quite a bit when he first released and I agree with a lot of what RoyAhoy has to say. Flashing blade iceberg does so much to help his damage output, as does res ploy. Desperation is bad; he wants more special charges and he can tank. Guard is good mainly if you want to bait Reinhardt or attack into QR tanks without one-rounding. Special spiral is the most aggressive try; mystic boost is the most ambitious option for a balance of offense and defense.
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