If you've got spare UtopiCoins it's worth visiting DonMai Sushi before a Ranking Boss Battle. From the "Eat In" tab you can buy different Sushi that provide character buffs. Recommendations: Tokujo Nigiri (revive), Nigiri (increased Health, Attack Power, and Tension). Make sure to go straight to the Ranked Battle after you consume because the buff is only active for the next encounter.