This page contains spoilers from the light novel! Read at your own risk.
- Before Meeting
Shin was always Lena's primary contact point for the Spearhead Squadron, as such the two would talk frequently over Para-RAID discussing both business and other topics. Shin was cold, curt and honest to a fault with the Handler; he thought of her as annoying and naïve. His opinion of her would change from her persistence in her cause, as well as from their time bonding over their shared link to Shourei. He would grow to respect her input and to be thankful of the things she had done for them, even something as practically insignificant as sending them fireworks. Shin would ask her to not forget him and the Spearhead Squadron during the Revolution Festival. In his final leter, he asked her to leave them flowers at their final destination.
His time spent talking to Lena left an impact on him, though he couldn't exactly understand his feelings towards her. When asked about the chance of Lena's survival, he deflected, to which Raiden noted he wasn't being honest with himself. 
Shin felt a burden was lifted from his chest once he managed to tell Lena that he was going ahead of her, as if he was finally free of his duty as the reaper of the Eighty-Six by entrusting their memories to Lena. This was the reason why he was devastated to learn that the Republic had fallen at the hands of the Morpho, and at the possibility of Lena's demise. Once again, instead of Shin entrusting himself to another, it would be himself that was forced to remember a fallen comrade.
Shin was surprised that the Republic had survived, even more so that an Alba officer was commanding on the frontlines carried by a one of her Processor's Juggernauts. As he did not know she was Lena at that moment, he thought of the things she had said—that she would continue to fight for her country and comrades—as awfully rich coming from the cowardly Alba. He interrogated her, asking for what purpose did she fight; only then did she reveal her name and her mission to reach the Spearhead Squadron's final destination.
Shin was relieved to learn of her survival. He did not reveal himself to be Shin, as he didn't want their reunion to be on the battlefield, especially after the effort Lena put into reaching their final destination. Shin figured she deserved better than to leave her mission incomplete by introducing himself.
Their second reunion at the Processor memorial was less confrontational. They regarded each other with a salute before Shin revealed their identities. He was still curt, but he wore a smile when speaking to her. It was through Lena that Shin was able to begin climbing out of his suicidal despair.
- After Meeting
Once Lena joined the Eighty-Sixth Strike Package, the two had to reset their relationship. They decided on a superior-subordinate relationship while on duty, and a friendship without the need of ranks in private. For the first time, they consistently referred to each other as Lena and Shin rather than Major Milizé and Captain Nouzen. Their relationship wasn't all fine during the start. Shin considered Lena to be shackled by the sins of the Republic which she did not commit; while Lena considered Shin to still be trapped in the Eighty-Sixth Sector, unable to search for a future beyond fighting the Legion. This lead into frequent awkwardness as one tried to confront the other.