Well, I gotta say that it isn't everyday that two beloved anison produced years apart share the exact same title. Therefore, today will be that special day. The one that I've already known about for years is "Omoide ga Ippai" by the folk-pop duo, H2O, the touching ballad that ended the anime "Miyuki"（みゆき）back in the early 1980s and has since become a graduation ceremony favourite, usually guaranteed to induce tears in the students.
"Ranma 1/2"（らんま1/2）is an anime that even I have heard about but only through reputation based on the original manga by Rumiko Takahashi（高橋留美子）. Even so, I have been listening to the theme song, also titled "Omoide ga Ippai" (Full of Memories) for the second entry of the anime franchise, "Ranma 1/2 Nettohen"（らんま1/2 熱闘編...The Fierce Fighting Edition）which went on for almost 3 years (1989-1992). The song often came up as part of my anime buddy's anison hour and I've got it in my collection of anison without having known its source for a number of years.
The aidoru group CoCo recorded the original version as the coupling song to their 3rd single "Natsu no Tomodachi"（夏の友達...Summer Friends）from May 1990. Written by Neko Oikawa（及川眠子）and composed by Masayuki Iwata（岩田雅之）, the cute anison sounds like something Misato Watanabe（渡辺美里）would have sung in her junior high school days; I think it is the synths that make me think that way. The single peaked at No. 3.
For me, the difference was just the added depth in DoCo's performance when they recorded it and that soaring instrumental bridge near the end. Incidentally, when asked how their collective name, similar to CoCo, was created, the answer provided was apparently that "D" was next after "C". Plus, there is the fact that the Japanese word "koko" means "here" whereas "doko" means "where".
Anyways, let's finish up with CoCo's performance.