Is a +SPD -Atk Hana Viable?

I could see it working if you inherited over Wo Dao+ and a fast Special...but if you're going to invest in promoting Athena or Karel to give the weapon to her you might as well just use them instead. Offensively, +SPD -ATK Hana looks quite similar to neutral Athena...so only go for it if you have an attachment to the character.

Give that LnD to another character, -Atk bane is awful.

If you are also planning on using her, you can get two neutral Hanas for free (better than having -atk), she can be excellent with Brave Sword+ and LnD.