Planning to make horse team, I'd put Reinhartd, Xander, Cecilia and... not sure about the last one.
For Gronnblade Cecilia I don't know if it's better putting L&D 2 or Fury 3, don't have access to L&D 3
Horse units apart from those ones:
5*Cain, Spring Xander, Priscilla
4*Stahl, Jagen, Abel, Peri, Ursula, Titania, Gunter, Clarine
3*Eliwood, Sully, Frederick
If you have your 2 buffers ( one with hone cav and one with fortify cav) , a blow skill is also feasable, either skill is good. If you plan on having a low life related B skill, like escape route, wings of mercy or such, you'll be looking at fury. If you need high health like a breaker skill, you'd prefer a blow or L+D. Though L+D often makes units too glass, you may prefer Death Blow for the extra damage.
I'd say the A skill will be dependent on the IV of your Cecilia - if it's an atk+ one I'd recommend death blow to maximise the single hit or Fury 3 for general stat buffs since she won't be outspeeding anyone anytime soon. Fury has the bonus of synergising well with Vantage
For spd+ variants LnD is arguably your best bet since that gets you to 40 speed (34 + 6 from cavalry buffs) which can actually outspeed a lot of things
For the last member of horse emblem I'd recommend another blade tomb mage (Ursula or Leo/Olwen if you can pull them), Eldigan (because honestly green mage checks are very beneficial since Reinhardt will literally kill everything else for you) or a dancer
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