Lewyn. Does he have a need for speed?

With Fury and Mystic Guard he'd be a pretty big pain for non-red dragons on both phases and still have offenses comparable to Swift Sparrow.

Fury and +Res is 32 Res, not shabby at all.

If you keep his default Odd Spd Wave, I don't really see too much problem with +Res (you get to 49 Spd with Odd Spd Wave active), except both -HP and -Def are superbanes, which sort of lowers the value of Fury, and you may be losing kills on offense where +Atk would kill.

He'd be able to bait Veronica with that set-up though.

If you did want a +Res Lewyn you'd probably want -Def for bane, actually.

You can never have enough speed with Lewyn. Go with +Spd so he can double literally anything and use the Flashing Blade seal even better. And then merge the other one into the +Spd Lewyn, as it will increase his speed by another point (at least, it did for me), but overall, go with +Spd.

+Spd, no doubt about it. He has no skills that guarantee doubles, so he needs the speed for that. You are correct, he is a pure player phase unit. He really needs those doubles if he wants to go against the triangle and KO fast reds like Ayra and Ryoma that also have low Res. (Don't mess with Caeda).

He ties Ayra for Spd, so if the Ayra is +Spd with DC, she wins. If not, he doubles her and she dies. This is a key matchup. A Spd buff or merges can get him the double against even a +Spd Ayra.

You don't want him tanking, because if you take any damage whatsoever, it can knock you out of Forsetti's follow-up range. This is especially risky with Fury 3. So really, you never want to use Lewyn in enemy phase, which makes +Spd and +Atk the only truly useful boons for him.

So definitely the +Spd Lewyn.

+Spd is his best option, in my opinion. Slap Flashing Blade and Blazing Wind and He'll have instant AOEs, granted if the enemy is slower than him by one point and/or have vantage.