Patronage.

When you treasure someone, you’ll try your best to protect them.

After Lenalee defeated Eshi, the voyage went on. When the team finally reached Edo, they encountered the Noahs, including the Millenium Earl. They confronted the exorcists. Lenalee, whose legs had yet to recover, was unable to activate her Innocence—let alone run for her life. However, her Innocence protected her, just like the time when she was drowning, it formed itself to be crystals surrounding her.

The Earl was interested when he saw this. He knew that her Innocence was acting strange. He came towards her, causing Lenalee so terrified of him. She was seeing unearthly hallucinations—it was just like one’s worst nightmare.

In the middle of her fear though, the prince on a white horse Allen saved the day. Rescuing Lenalee was the first thing Allen did in his arrival to the battlefield. He came from behind and greeted the Earl. Upon hearing his voice, Lenalee turned her head to Allen. At first she looked surprised, but then the look on her face expressed a relief—that he finally came back, and that she was protected.

Chapter 111. a Tease approaching Lenalee

The Earl retreated, and the team stumbled upon other rooms and some battles with the Noahs. And finally, they came to a room where Road and Tyki were waiting. Tyki was wondering about how Allen could have survived and even recovered his Innocence—he was supposed to have died because of Tyki’s Tease! A Tease then approached Lenalee. Allen stabbed it immediately before it touched her.

"Tyki Mikk, I have to say something as well. Any more than this... if you lay a hand on my comrades... I may end up killing you. Lenalee, believe in me. I will definitely... take him down."

Chapter 111. Enraged Allen

Allen was aware what would happen if that Tease were to do the same thing it did to him back then. The look of his face had totally changed. Before, he tried his best to control himself while talking with Tyki and Road, but since Tease came to Lenalee, he couldn’t keep his cool anymore.

I love how Allen still paid attention to Lenalee even when he was having a conversation with Tyki. It showed how he was aware of her, and trying to protect her from danger. His patronage to Lenalee looked like something he'd do to someone beyond friends—more of a special person.

While we're talking about patronage, in most occasions you probably find that Allen was the one who did more defense, compared to Lenalee. And that is also the reason why some people claim that Lenalee was the damsel in distress archetype. This is not the case, actually. The reason why Lenalee was often being the "defended" one was because she couldn't use her Innocence. She might seem useless because all the Noahs were coming when she was an exorcist who couldn't even activate her Innocence, but really? She actually tried her best to do something on her own instead of staying still, just waiting for protection.

You can see that there are also moments when Lenalee was the one who protected Allen. Once she was able to synchronize with her Innocence again, she was the first person who came to rescue Allen during the akuma infiltration.