The pattern is based on the positions of the letters in the English alphabet.
- JMSU: Letters are 2 steps apart (J to M, M to S, S to U).
- IMPV: Letters are 2 steps apart (I to M, M to P, P to V).
- YTSR: Letters are 1 step apart (Y to T, T to S, S to R).
- AEKM: Letters are 4 steps apart (A to E, E to K, K to M).
The odd one out is "AEKM" because the step difference is 4, unlike the others, which have consistent differences of 2 or 1.
Therefore, the correct answer is "AEKM."