Most recent case of WTF from Touma losing his arm at the end of New Testament. Touma is split into two versions, the real one and a devious copy of him made from the dregs of whatever is within Imagine Breaker. Said fake takes his Imagine Breaker while the real Touma gets turned into a dragon.
Later on, we find out this manifestation was made from Touma’s negative aspects and subconscious wishes. As a result, it even retains the memories he himself lost that he wishes he had which wrecks havoc on Shokuhou for reasons too long to explain.
Long story short, Shokuhou and Pre-memory loss Touma have a history together and circumstances lead to Touma not only unable to remember her but also to immediately forget about her the moment she leaves his sight. The copy takes advantage of this from possessing those memories to manipulate her.