[Raigen.Convict]

Let me be the first to say this is a BAD idea. Leveling youkai to 70 using destiny summoner is a bad idea mainly due to the accessibility of so many options to actually make the combo busted, not only do you have the availability of a slew of spells and skills due to 12 youkai active max, you also have the ability to use fast offense to make each summon act immediately on top of using Grand Summoner to allow you to, so long as you push at least 1 target back, reduce summon momentum cost making the youkai hit even harder than they already do from having the buff of synchro summon and fast offense, meaning you can burst someone down to nothing for almost no effort, and have a way to revive the youkai as you please, too with Reihou, AND can heal them and yourself using Healing Discharge. Not to mention access to ritual sword even without a bonded youkai to keep your fp steady, and judgement blade's capability to use a sword cast tool. and let's not ALSO forget that you can use encourage to also buff your youkai even FURTHER when NPC's do not encounter diminishing returns.... Seiryuu on its own achieves 48 defense with no buffs of any sort at level 60, so add in +5 from dragon affinity, +6 from synchro summon, +5 from encourage, possibly 6 with a white spirit and you have 64-65 defense on that youkai WITHOUT EVEN GOING INTO LEVEL BONUSES YET. Not to mention Hunter winds hunted level is Seiryuu's level /2 meaning 70/2 equalling out to 35% instead of 30%. This may not seem significant until you add in the warpaint prayer which increases the level of hunted inflicted by you by its level which is 5 if I recall totalling out to 40% extra damage. 40% extra damage for free is no laughing matter on a youkai who's scaling will be increased even FURTHER, potentially back to the 350% elemental attack that they were nerfed from for balance reasons. And this is just math on ONE youkai... This is just one thing out of 12 that would be accessible to you. Sure, you can outrun them but then the summoner just calls them back and you either have to watch them suck the fp from thin air to rejuvenate and the fight goes nowhere, or try to hit them from a distance which can be lessened through the use of install and drowned woman if not using elemental damage.
tl;dr knowing the synergy actually present in Summoner Destiny, this is not a buff we want.