In a small sauce pan, whisk the soy sauce, syrup, vinegar, ginger and garlic powder until combined.
Heat on medium-high heat until it just begins to boil, then reduce to a simmer.
Whisk the corn starch and water together in a small bowl until fully combined. Whisk into the teriyaki sauce for approximately 30 seconds or until it thickens. Remove from heat.
Notes
Store in an air-tight container in the refrigerator for up to a week. See the notes in the post to learn how to customize your sauce.