Moments pages are spoilers off; beware of unmarked spoilers!
The relationship between Shouzou and Ine in its entirety. They've been together for more than half a century and are clearly still in love with each other as much as when they first got together. They treat each other with respect and care. Shouzou even specifically mentions in Chapter 86 that the two of them ensured there was no imbalance or a stereotypical wife taking over the housework relationship. Especially back when exactly that was more common, if not expected.
When Shouzou turns back into an old man, Ine remains young. Shouzou believes Ine would much prefer him as a handsome young man, but she's quick to tell him she fell in love with him as a person; not young Shouzou or old Shouzou, but the man named Saitou Shouzou.
Heisuke decides to keep the chest that his deceased wife's personal effects were in while the storehouse is being cleaned out. Most of the stuff is considered old heirlooms or things collected by his own grandfather, but this one thing he's clearly not ready to leave behind.
After Ine loses her memories and mentally reverts to a time before she met Shouzou, there are still implications she remembers her love for him. When he seems disappointed, she notes a strong urge to take on some of the burden.
When she finally regains her memories. when Shouzou had to go for a meeting, Ine felt anxious without his presence. That's when her memories started to flow back. Particularly when her relatives refused to let her see him due to bad blood between their families, and Shouzou begged to let Ine's family see her, even in the rain. And when Ine fell ill, Shouzou did everything he could to care for and pay for her treatment. Even when she tried to dissuade him, he assured her that he'd always be there to make her happy. In the present, once Shouzou returns home, Ine happily embraces him with her memories restored.
