Ok I will give out the answer, so that we can continue with the game...
The odd one out among Indra, Vayu, Surya, Bhoomidevi and Agni is according to me Agni since all the other four had children connected to both Rama and Krishna.
Indra -----Vali and Arjun
Surya----Sugreev and Karna
Vayu--- Hanuman and Bhima
Bhoomidevi---Sita and Satyabhama
As far as I know, Agni did not produce an offspring connected in any way with Sri Krishna. (Of course, I did not count Draupadi here...I did not think Agni to be her 'father'
Anyway, your reasoning was also correct and better than mine... So you win 👏and it is your turn to ask the next question ...