Legendary Ike

What I have in mind was making Ike, like in Path of Radiance where he was able to solo the game Lol.
Mine is +5 merged, + def and summoner support. I think, if you have a + spd will work better, he will be able to avoid some doubles and make his own, specially against those annoying dragons (Except for Winter Sothis, she is too fast, but a Aether with wrath and she is death). L Ike + spd at +10 without summoner support and draco flowers can reach 37 spd and with teammates who can speed buff, he can go further to the point where QR sacred seal will not be needed. Without merges he is at 33 spd, it is still good.
Now the build:
- Weapon: Ragnell, Distant Counter on a weapon is always great.
- Assist skill: Reposition because it is cheaper, but a Rally+ or Harsh Command+ is better if you want to score more arena points.
- A slot: Atk / res solo or his warding breath. I prefer Atk / res solo because it works on both phases and Ike get a +6 invisible boost in atk and res.
- B slot: Wrath. when active, he is able to defeat so many units, even blue ones and will restore full hp or almost thanks to his Radiant Up B (Aether).
- C slot: Rouse Atk / def. A +6 visible boost in attack and defense. Ike will have a great mixed bulk thanks to his C skill and A skill, also he will have a +12 in atk. The problem with this skill is the activation, Ike must be alone in order to use it.
- Sacred seal: Quick Riposte or Distant / Close defense. QR is in my opinion more usable for him when he is not a + spd and +10. That double is needed, but if Ike is +10, + spd and +10 dracoflowers you may change it to Close or Distant defense to make him more durable than he already is.
Conclusion: Even if my Ike is not a +10 and + spd, this set works amazing on him, for arena and every other mode it works great. You shoulg give it a try if you like it.

W - Ragnell: DC weapon
A - Reposition: Standard assist
S - Radiant Aether: Aether at 4 special charge
A - Warding Breath: Special charge +1 and res +4
B - Quick Riposte 3: Retaliate with a double
C - Def Tactic: Filler skill
SS - Close Def 3: Increase close range bulk

Stats higher than usual due to summoner bond (+5 HP, +2Atk/Spd/Def/Res), + 1 merge, and +3 dragonflowers

Weapon: Slaying Edge+ (Def+ Refine)
Support: Variable
Special: Radiant Aether
A Skill: Distant Counter / Steady Breath / Warding Breath
B Skill: Special Spiral / Quick Riposte / Swordbreaker
C Skill: Variable
Sacred Seal: Darting Stance / Quick Riposte / Quickened Pulse

An incredibly high investment build, but hear me out. If you really like Ike I think this is the ideal build. It reduces his unique Aether thanks to Slaying Edge+ but also pads his stats some more thanks to weapon refinery.
By switching out your weapon and A skill you lose a net 2 attack but gain a special cooldown charge (retaining Aether proc retaliation), 5HP and whatever refinery buff you choose (speed to avoid doubles?).
Ideally he would have an ally providing infantry breath to him to further reduce special cooldown on the first enemy phase.
and thereafter special spiral 3 in hid B slot should cover the rest.
If highly merged darting stance can avoid critical doubles whereas at lower merges quick riposte is your best bet.

One cheese shenanigan you can run is Slaying Edge+ (refined), Steady/Warding Breath, Wrath and Quickened Pulse Sacred Seal to make him an almost unkillable enemy phase melee brawler

It's an +4 with a boon +ATK

A: Warding Breath, it give him some bulk against magic user in combat and lower the cooldown.

B: Vantage, it gives him the possibility to attack before the enemy which safe me several time even more when he's special was ready.

C: At the time, I didn't know which C I should give to him so let's reduce the enemy def...

Seal: The combo Vantage and QR is deadly for this kind of unit who can heal themselves.

This build is an enemy phase all purpose build for all game modes. Ike built this way will have 37 def and 33 res (for Distant attacks) with summoner support,
which enable Ike be able to tank most units just by himself, and since he normally receive some ally support it will make him even harder to kill.

Even without ally support this Ike will be able to tank 1 hit from all units and 2 hits from most units except blue units with very high atk (physical units with atk >= 50 and magical non-dragon units with atk >= 47).
If Ike is not killed he will then always counter attack twice thanks to Quick riposte and will always active Radiant Aether on the 2nd hit (or 1st hit if enemy unit can atk twice before Ike can counter) thanks to Warding breath, dealing substantial damage to the attacker and healing himself.

For e.g. a Reinhardt without boon and has life&death as A skill will have (32+9+5)=46 atk, and will atk twice dealing 44 damage to Ike (46*1.2 - 33)*2, and Ike will then counter twice and defeat him, with the first atk being radian aether and heals himself for 40hp.

Typical use of this build would be for an player phase ally unit to initiate the combat, and then have Ike use reposition to move the unit out of harm and wait for enemy to engage him. For e.g. I use Brave Veronica as Ike's support, with good positioning she will reduce enemy's atk by 4, buff Ike's def/res by 4 and provide Ike with 2 def/res support bonus, enable him to tank and counter everything except specific blue units (e.g. bold fighter armors).

His C skill is quite flexible, I left his native Def Tactic 3 as it is quite useful in many situations to prevent allies getting OHKOed.