I can't type in kanji at the moment but I love you is "Aishiteru (wo/yo)" the difference with wo (written in romaji as o ) and yo , is that aishiteru wo is also used by males directed to a female, and aishiteru yo by a female vice versa. The more formal I love you is "Koishiteru" as Koi means love as well. Sometimes you can use "Daisuki (dayo)" to express extreme liking to someone too, it's also common in confessions :D especially in Anime~~