Henry is the thirteenth playable unit. He makes his appearance in Chapter 13. His birthday is November 13th. Thirteen is absolutely an important number for Henry. Were these thirteens coincidental or planned? Are they supposed to represent fortune or misfortune? We can't know for sure. As far as I know, the developers of the game haven't talked about the significance of the number thirteen to Henry. I think there are too many thirteens surrounding Henry for it to be a coincidence, however.

The number thirteen isn't really significant in Japanese superstition. This is important to note because the game was made in Japan. Any supposed misfortune around the number thirteen would have come from western influence. In Japan, the numbers four and nine are considered unlucky because the words for those numbers are pronounced the same as the words for death and pain respectively. The number thirteen is not unlucky to most Japanese.

It's not hard to see how the developers of the game might have been influenced by western superstition, however, or why they would put it in the game. They have a large western customer base, and released the game worldwide.

In the west, the number thirteen is considered unlucky for many reasons, many which stem from mythical or religious reasons. In Norse Mythology, an honorary banquet was held in Valhalla for Baldur, among twelve other Norse gods. Loki was an uninvited thirteenth guest. In Christianity, Jesus' last supper had thirteen guests. It's easy to see why many think the number brings misfortune.

The number thirteen is used in a wide array of horror films and stories and is universally considered dark. Henry is a very dark character with a very dark past. I think if anything, the game developers wanted Henry to be themed dark, and went with thirteen because of how it was used in popular culture.

Oddly enough, his birthday, November 13, is World Kindness Day, a holiday recognized by many countries around the world, including Japan. The holiday was created to inspire people to build bridges between divisions of race, religion, and sex, and be kind to one another.

In Henry's Support with Panne, Panne calls Henry a filthy Grimleal craven. Henry says,

Henry: That's not very neighborly, now is it? What difference does one's religion make? I just want to be friends!

That kind of embodies the purpose of World Kindness Day. In fact, Henry embodies it altogether. He is one of the few characters who don't see others by what side they are fighting on, or what they believe. His best interactions are with people who aren't conventionally normal or accepted: Nowi (a manekete), Panne (a taguel), Cherche (a foreigner), etc. Henry isn't exactly immediately accepted or considered normal himself, but he is quick to be kind to others.

What if the significance behind the number thirteen in relation to Henry wasn't sinister at all, but is there to draw attention to a nicer part of Henry, his kindness to those he gets close to? That's pretty cool.