I usually stack buffs constantly in my SMT games, but I haven't really felt it as necessary here. I stuck Nocturne's broken Fog Breath onto my MC and haven't used it at all despite being two debuffs in one. Even Tarukaja, my go-to, isn't really as, er, go-to.
Edit: Admittedly, this may be my own fault. It's pretty easy to make a brokenly powerful magic-using MC without much effort. He doesn't need buffs to dominate every boss.
Recommended fusion for everyone: Parvati.
She lasted me some 15 levels and still ended up with a higher magic stat than level ~40 demons by the time I retired her because her low HP started hurting her performance.
Also, if you like mages:
Save ~70 App points for when you hit 30 and you can buy a MP recovery while walking App for all of your demons.
This thing is so broken, you'll never run out of MP.