Atk/Spd bond 3

Off the top of my head, Hana

- Felicia (as well as Innes, who is not easily mergeable, and possibly Kaze, who is now in the 3*/4* pool)
- Owl tome users, because they're trying to stand next to allies to boost their stats anyways
- Somebody using the flier formation seal or B-skill, because the bond activates whenever you warp using this skill
- Fliers in general...I think Camilla is probably pretty good with it
- Mixed phase units, especially those that like to have their A-skills active from the start of the battle (and therefore don't prefer brazen skills). I wanted to say light breath Fae, but that's a pretty marginal case because her def is a bit low. +spd M.Grima receiving hone armour, for example, reaches 68 atk 38 spd with the bond active, so you can play for one-shot on player phase and try to avoid doubles on enemy phase, maybe even go -def because HP is mixed bulk if you only get hit once. +spd Nowi with lightning breath +spd can also try this, especially with team support. 38 spd at 0 merges before any buffs. You would have to give up using a breath skill on her (so probably no aether; it just takes way too long with the cooldown penalty on the weapon), but you'll probably block quite a few doubles so it compensates for having less def and res until some bold fighter initiates on her.
- Armours? Because they like to clump. Draug has good speed; he could potentially use it.
- Offensively-minded healers that aren't dependent on pain+ double sb, because their A-skill selection is relatively restricted (no fury, no blow skills, etc.) Elise is the quintessential example, but she's hard to merge, so you're looking at Clarine, Priscilla, Maria, and maybe Serra. These do have the potential to withstand a counterattack from a DC unit (it will hurt, but if you use martyr+ that becomes an advantage, and if you're scared then stack live to serve on it and maybe use a dancer) so if they take wrathful staff refine, in combat they have close to if not 50 atk with atk boons, before buffs. Clarine and Priscilla are mounted, so if they receive hone cavalry they can actually get quite aggressive.
- Virion, if you want to use him to bait archers and daggers (though baiting daggers is often troublesome due to the debuffs)

That's all I can think of right now. The other examples are not easily mergeable (Y.Tiki, for instance, with her new prf)

There's a build I'd like to try using Lon'qu;
Wo Dao+
Moonbow
Atk/Spd Bond
Wrath
Infantry Pulse

A bit expensive, but it would be a pretty good build, I think.