This is the 2938th most frequent Turkish word.
seni
"You."
In this sentence, 'seni' is again the accusative form of 'sen', used here to represent the direct object of the verb 'saw'.
Seni dün parkta gördüm.
I saw you at the park yesterday.
'Seni' is in the accusative case, showing the person being thought about, as the complement of the verb 'thinking'.
Bu şarkıyı seni düşünerek yazdım.
I wrote this song thinking about you.
Here, 'seni' is the accusative form of 'sen', indicating the direct object (you) in the sentence.