is jujutsu kaisen episode 31 filler?

Kokichi Muta — Mechamaru — fights Mahito. Kokichi spent his entire life controlling puppets from a distance due to a Heavenly Restriction that gave him incredible cursed energy range in exchange for a body that couldn't function normally.

He traded information to Mahito's group in exchange for healing his body. Mahito kept the deal.

Kokichi felt sunlight for the first time, then immediately activated Ultimate Mechamaru and tried to kill Mahito. Seventeen years of stockpiled cursed energy wasn't enough.

Mahito killed him. Ten days later, the Shibuya Incident begins.