What to do with +Atk -Spd Hinoka?

With Hinoka's Spear and Death Blow, she would command 63 atk and only 33 speed while she has an infantry or flier near her. That's before counting buffs. If you were to then have a pair(or trio) of goad flier allies, her atk and speed become 71 and 41(or 75 and 45 respectively) I think if you run her with some Goad Flier allies and a Spd + 3 seal, she can fight quite effectively.

Alternatively, you could trade Death Blow for Fury, Lose 3 attack, gain 3 speed/def/res. Then with 2 Goad Flier allies and the +speed seal, she's rocking a fantastic mix of 68/47, with her defenses sitting at a passable 28/27. Replace Lancebreaker with Desperation and that's good to go.

Even without access to Goad Fliers, she can still get some significant gains from NY! Azura. 64 atk, 39 speed before counting A skill or Seals, 67/42 with Fury, 67/45 with Fury and Speed + seal. With all the buffs she can get even from just 1 ally, her +atk is a nuke, and her -spd is very much reparable.

Ok, having a second Hone Fliers user is a great start, since that'll bump her 29 spd up to 35.

Add +4 from the Hinoka's Spear since she'll be near New York Azura. That's 39.

Fury and Life and Death are good on her, depending on which you have more readily available.

Then add Fury or Life and Death, putting her up to 42 with fury and 44 with Life and Death.

I don't even need to do the math for her attack, it fucking skyrockets with her +Atk. Mine ends up at like 70 attack with the proper buffs.

TLDR she'll be fine, just slap the Spd+3 seal on her and Fury or Life and Death. Hope I helped!