Ruff Tuatha Dé

Ruff Tuatha Dé is the deceased older sister of Lugh Tuatha Dé.

Background
According to author Tsukiyo Rui's Twitter post (14/10/21) following episode 2's release, Ruff is born of Esri when she's just 15, one year after marriage (14). Ruff passed away at the age of 12, with reasons still currently unknown. In the same year, Lugh is born.

Trivia

 * Although never specifically mentioned, Esri's current age in the LN can be derived from the information of Ruff. Esri married when she's 14 and gave birth to Ruff when she's 15. When Ruff is 12, Esri being 27, Ruff passed away and Lugh is born. So when Lugh turns 14 in book one of the LN, Esri is supposed to be around 41, though in book five after months passed since book one, it is stated that her age is approaching 40, a likely mistake by the author.


 * Above information from Tsukiyo Rui's twitter post.(https://twitter.com/Tsukiyo_rui/status/1448324606679420932)