A post on yahoo!answers gave me the gumption to do a full translation of this song; had I been a little more savvy, I'd have noticed that the answer was 'closed'. No worries, though, it's here for posterity. A few disclaimers and it's on with the show (you can always skip this introduction and just scroll down to the song).
First, I'm only guessing that Aiko sings this to someone in particular in first person, though it seems highly likely. My verb forms aren't very precise, and it's possible that I'm waay off the mark on some of this. However, the romaji is correct, disregarding the spaces between some words (and it can vary sometimes, depending on the translator.)
I try to make my translations follow the original text as closely as possible, so that the English wording is aligned with the Japanese wording. I never combine two lines to make a more fluid sentence structure. Because of this, however, it's easier to pick out the source word(s) and come up with a more precise meaning on your own.
The romaji is a modified Hepburn style which should make sense to beginners and experts alike. The perfectionist in me wants to have it in 'kunrei-shiki' style so that it can be back-translated, but it's harder to sing along with. So all my romaji will be in this style, for future reference. I won't be mentioning this again in future posts, but just so you know.
Last, unless it infringes on other applicable laws, I hereby release the romaji and translation to the public domain, to be used in any way, by anyone, for any purpose. If you repost, please also provide the songwriter credits. Thanks!
solitude
(romaji/translation)
as sung by Kayo Aiko
lyrics (Japanese): Kenn Kato
composer: Y@suo Ohtani
arranger: ats-
chorus arrangement: YAS KITAJIMA
aitakute (i miss you)
aenakute (i want to be with you)
nantonaku uwa no sora de (for some reason i'm preoccupied)
kizuitara muishikini anata wo omotteru (before I know it i'm unconsciously thinking about you)
sou kitto (yes, undoubtedly)
mou zutto (the whole time)
kotae nara wakatteru yo (i know the answer)
sore na no ni akirame kirenai kute, gomen ne (despite that, i must apologize)
hito wa naze todokanai hodo (how can a person not reach their limit)
oikakeru no kana (i wonder if i'm getting through)
saki ni nagedashita no wa (before i throw it all away)
kono watashi, sore na no ni naze (me, despite all, how can i?)
deaeta hi no yasashisa mo (we meet on days with gentleness)
kasaneaeta nukumori mo (overlapping with warmth)
motomerareru yorokobi mo (i'm wanting joy)
maboroshi ni wa omoenakutte (this vision is unlikely)
uso da toka (a lie such as this)
himitsu toka (a secret such as this)
shinjirukoto mo wasurete (i believe i'll forget)
otagai ni samete risuru you ni natte ta (it reaches the point where we blame each other)
hito wa naze fuan ni naru to (why do people get nervous)
shibari tagaru kana? (wanting to tie together, i wonder?)
sore ga touzakeru koto (i guess staying away is a fact)
shirinagara tomerarenai ne (i can understand, but it doesn't end)
jiyuu toka kodoku da toka (if it pleases you, have solitude) ["kodoku"="solitude"]
naimono ne dari de kawaru (it's asking too much for change)
honto wa dochira mo onaji (really, we're both the same)
sou kokoro wa wagamama da ne (because our hearts are selfish)
wakare no hi no samishii sa mou (the days we're apart are sad)
kizutsukeau kanashimi mo (this wound is sorrowful)
kuyami kirenai itami mo (condolence can't be hurtful)
futari dakedo shirushi ni naru (the two of us will get a sign)
hitotsu hitotsu omoide wo dakishime (one by one i hold the memories close)
aruite iku kara (we walk along)
warainagara furimukeru toki ga (we are smiling, the time to turn around)
kuru you ni... (so that it becomes)
zutto... (always)
deaeta hi no yasashisa mo (we meet on days with gentleness)
kasaneaeta nukumori mo (overlapping with warmth)
motomerareru yorokobi mo (i'm wanting joy)
maboroshi ni wa omoenakutte (this vision is unlikely)