The Dark Pictures Anthology: Man Of Medan

If this is your first playthrough, just progress through the story until Alex and Julia go diving and you gain control of Fliss.

If you have already beat the game and managed to miss this achievement (Like I did!), go to Scene Selection and load "Uninvited Guests".

In the beginning of this Chapter, Conrad tries to flirt with Fliss. Choose these dialogues:

Relaxed

Self Assured

Uninterested

After the short cut scene, go to Conrad and then press A to talk to him. Now all you need to do is to select these dialogues:

Stern

Curious

Romantic

Good Luck :)

This one is easier single player. As Conrad, flirt with her and as Fliss flirt back. The final conversation takes place when she says that she needs to tend to the ship. Talk to Conrad and select "Romantic" as the conversation option.