Blessing is a new feature added to Fire Emblem Heroes with the introduction of legendary heroes back in end of November 2017. If a hero is conferred with an element, then during the corresponding season, the hero can be 8 points stronger if goes in battle with the corresponding legendary hero. Blessing seasons are in sync with Arena reasons that they cycle on every Tuesday.
Here is a list of blessing seasons in the past for your reference:
11.28 (Tue) ~ 12.4 (Mon) Water earth. Fjorm, the legendary hero of Water
12.5 (Tue) ~ 12.11 (Mon) Water Wind
12.22 ~ 12.18 Fire water
12.19 ~ 12.25 water earth
12.26 ~ 1.1 water wind, Gunnthral, the legendary hero of Wind, out on 28th
1.2~1.8 Fire wind
1.9~1.15 Wind earth
With this pattern, 1.16~22 would be Wind, water, 1.23~29 maybe Wind Fire, which is likely to be the January legendary hero reveal date. It implies that the next legendary hero would be fire, corresponding to red, and the last one in Feb would be earth, corresponding to colorless. There are 2 movement types left, armored and flying. It would be rule breaking if they introduce a flying bow or dagger user. Or armored healer who can carry Ward Armor. I guessed they’d have one who can dance, but since Azura can already fly, it’s more likely to be a flying healer or ranger in February. Either way, I’d like that new legendary hero to join my force. If it’s a dagger user, it would be a usable one to debuff for Gunnthral but not occupying the previous spot to hit enemies.
Another fact revealed by the schedule is, if you want to cover all time, you need at least 3 legendary heroes and their corresponding teams (blessings are consumable so it’s not recommended to switch).
The tentative red armor unit would be strong too, stronger than Zelgius to draw whale’s attentions. But seriously, I think both Winter Tharja and Zelgius are pretty broken already.
The armor and flying legendary heroes will boost def and atk of blessing conferred units. We don’t know who will get what yet.
