Jashi was a well written couple to me and here is why.
The parallels between Ashi’s childhood and the scenes with Jack mirrored plot points leading up to Ashi’s Redemption.
The ladybug symbol - Which if you didn’t know is a Japanese legend where if a ladybug lands on you and you let it go it lands on your soulmate or true Love.
Time constraint - Animation takes time, and buget I’m sure Genndy had more scenes with Jack and Ashi but, he had to cut some of them because of time or buget.
The opening monologue - I feel like people didn’t pay attention to the beginning monologue for season 5 at all he said Fifty years had passed but I DON’T age time has lost it’s effect on me..so that means he is still the age he was when the show started.
Jack’s innocence - Yeah one of the big complains is that they are awkward or it feels awkward. It only feels that way because Jack didn’t have much experience with Romance before. And we aren’t used to Jack being this way around Woman.
It is awkward because this is the first time any of them has been in love so they are acting like teenagers and that is okay.
Change in tone - Season 5 is a lot more adult and handles darker themes as such romance will be taken more seriously. Before Samurai Jack was for younger audiences and kids would not be interested in romance but now that the audience is older Genndy thought they were ready to be told romance.
The visuals - Genndy is really good at visual story telling and tells the part of the story behind hidden geatures go back and watch their body language I think you will find subtle. Gestures.
The performance - Phil La Mar and Tara are phenomenal at petraying the chemistry that Jack and Ashi bulit together.
They saved each other - Jack saved Ashi from death and for the darkness and Ashi saved Jack from depression suicide and helped to renew his purpose to return to the Past. I don’t think Jack would have returned to his mission if it weren’t for all Ashi.