If you mean "summoner" like "summons egis of primals", then your character has to have been present at the defeat of the primal in question in order to summon that egi. For this reason, being able to summon more than one type of egi is probably kind of rare.
I say so because I don't know if you intended to include such a thing in your character's backstory, or if you just thought it would be a good way of him venting his excess aether. In that second case, I'd recommend Carbuncle - maybe a custom geometry specifically intended to siphon off extra aether from the target (your character)?
If you did intend for him to have defeated Ifrit/Titan/Garuda in the past, then carry on!
I say so because I don't know if you intended to include such a thing in your character's backstory, or if you just thought it would be a good way of him venting his excess aether. In that second case, I'd recommend Carbuncle - maybe a custom geometry specifically intended to siphon off extra aether from the target (your character)?
If you did intend for him to have defeated Ifrit/Titan/Garuda in the past, then carry on!