Question on how to pull a specific focus unit...

It's a bit counter intuitive, but I'd say pass on the blue orbs, and pull on greens.

First; you must make a summoning contract with a lesser Sacred entity, preferably a stone of some kind.

Then, you must pull from every color, because confirming that you have the only logical answer is pointless.

Then, you must have at least one Eirika, just to welcome her brother home. Send home an Innes if you must. And finally, make sure that he has plenty to fight.

Just prepare a saxophone and get the rest of the Grado's musician together, also a good garage so they can play.

Don't know the Math, But I think that the blue orbs will have the highest chances to pull a 5* with red the lowest but it might have a higher chance to get a 5* on red cause there are 2 units that are in the color.

Beat RNG into submission ...with the power of your wallet !!!

(or purse, whichever is applicable)

I found out that sniping is the best thing to do.
Doing full summoning session is only best for 8% banner.
So snipe for blue, if there are no blue then you have to try one other orb that can still be good for your barracks (idk, you have few greens, worst that happen you get pitybroken by a green that can be useful, or merric)