The drink in this episode is called the Slim Reaper. Watcher gives the recipe:
2 tsp matcha
2 tbsp hot water
3/4th cup oat milk
3 tbsp Nigori sake
2 tbsp simple syrup
In a tea bowl, whisk matcha with hot water for ~1 minute. I've found that optimal stirring motions include a figure 8 mixed in with some circular action. After that's complete, stir in the simple syrup and then pour that over the oat milk. Finally, mix the latte with Nigori sake and pour the final drink into a cup of ice.