Except for vague inferences from character lines, there are no "romance" possibilities for any pairings. Onigiri are the traditional Japanese food gift, similar to a cookie. They are small, easy to carry, and contain little room for error or confusion with another item on the plate. Thus, they are perfect for showing someone you care. Onigiri are traditionally made of rice flour and seaweed, but other ingredients can be used instead. Sugar is usually added to make them more tasty and nutritious (because rice is already very healthy). There are many different types of onigiri, such as vegetable, seafood, meat, noodle, and fruit ones. They can also be filled with vegetables or meat. Since onigiri are small and simple, there is no real restriction on who can give them or what could be written on them. You can use this opportunity to show your friend that you care about him/her by giving him/her some onigiri with which you enrage him/her slightly (but not too much) by putting something strange in it. This will make him/her laugh, which is good because it means he/she is doing well even if you aren't around to see it.