But in bed, I'm a tuna.
To call someone "maguro" (tuna) when it comes to sex means that they just lie there and don't do anything. It may come as a shock to see I'm a total pacifisht.
"Sabasaba shita seikaku" means a person who is easygoing. I have no idea how else to incorporate this fish pun. Even though you're a wakasagi!? Even though you're a wakasagi!?