Probably warmaiden. Take my answer for a pint but her bc khatun is great for speed and seeker is just great.

Keep  Warmaiden  for  her  aoe  Def  down.  Replace....  well  it  could  be  either  Elhain,  Seeker,  or  Khatun.  

If  you  can  gear  Big  Un  well  enough  he  can  be  all  the  nuke  you  need,  so  wouldn't  need  Elhain.  

Or  you  need  to  decide  if  you  want  Khatuns  speed  or  Seekers  +Attack.  

I  would  personally  replace  seeker  for  now.  I  remember  my  first  nukers,   needed  two  to  get  the  job  done.  

replace elhain

Replace  Elhain.  He  has  the  same  role  but  better.

Definitely replace Elhain. You have a very good team, all you're missing now is a better speed lead. Once you get Arbiter you'll be set.

Replace  Elhain

Big  Un  is  a  better  nuker  vs.  Elhain.

It  is  an  upgrade.

You  want  Big  Un  in  Savage  +  Cruel  gear  if  you  can  manage.

It  would  be  ideal  set  up.

If  you  can't manage,  You  will  want  him  in  your  best  blend  of  damage  dealing  gear.

-  C.Damage

-  Swift  Parry

-  Affinity  Breaker

-  Fatal

-  Divine  Offense

-  Offense

If  all  your  gear  set  pieces  are  crap,  You  should  run  broken  gear  set  pieces.

The  goal  is  to  increase  Big  Un  ATK  +  C.RATE  +  C.DAMAGE.