Go for Heat
While most baths are warm, a number of ways exist to create more heat during the experience with your mate.
Instead of the cliched bubbles, try for a scented bath oil. After the bath, dry each other off with some warm towels right out of the dryer. Then, you can rub some heat-activated lotion on each other's skin. If you have no heat-activated lotion, empty a little bit of lotion into a microwaveable bowl, heat for 10 to 20 seconds and then enjoy.
The Japanese take bathing very seriously.
Most will soak in a bath once every day. One difference between the Japanese custom and Western custom is washing before getting into the tub. So, make sure to wash before submerging in the water. The water should be as deep and hot as you can make it. There is no need to put anything into the water, but feel free to use some Oriental-inspired oils. Light some Oriental incense and place in the bathroom. If you have a suitable tray, prepare some green tea and serve out of traditional Japanese tea cups during your bath. If you are a woman, you can go all out and act like a geisha. Dress yourself in a kimono or any robe and squeeze water onto your man's skin from a loofa or a sponge. Or, if you want to get into the tub with him, paint your face in traditional Japanese fashion and pin your hair to your head with chopsticks. Then, you both can squeeze water onto one another.
A traditional romantic bath would include bubbles, soft music playing in the background and candles all around the bathroom.
Make sure the water is extra warm and the bubbles are plenty. Rose petals can be strewn in the bath or a pleasant scented oil put in the water. You can up the ante by serving one another champagne and chocolate-covered strawberries.