This is a strange question to answer because of the nature of collaborative roleplay. Logical in-character paths often won't pan out because of out-of-character realities, be those the necessity of being able to stay in RP or because some fresh NPC takes the place you've destined for your character. Star Army characters who raise to admiral rank, for example, become NPCs that are usable by at least Wes, and not everyone wants that for their character.
So, realistically, Ketsurui/Kitsurugi Aiko in 20 years will still be the first officer or captain of whatever ship features in the Kaiyō plot. Ranked Taisa at max. There's plenty of room in that space for her to continue being a renowned warrior and hero of the Empire. That is simply if the OOC status quo persists because the plot must go on.
In a fictional reality less bounded by a roleplay's OOC necessities, I think she'd become a Taisho of one of the Star Army's fleets 10 years from now. Even before that, she'd probably become a brevet admiral in the Star Army of Uesureya simultaneously to her Yamataian rank. At some point in her life, Aiko would be the shogun/military governor of a Yamataian sub-sector. And then grander beyond that, eventually leading a full nation because it's in her character, but there's really no timetable associated because Neko/Yamataians are effectively immortal and so 20 years is a footnote in personal/professional progression. She'll teach at SAAMMS again, as she has in the past, to confer her experiences upon newer generations of military leadership.
My other character, Saiga, would probably be a retired family man in 20 years. Tending to some Saiga Clan castle and the responsibilities therein. His in-character goal starting in 2005 was to become a SAINT agent and, logically, rise up to one day become Director. But I don't want him to be an NPC so that's out for whatever will happen in actual RP.