Diestat Noumou is an aged and learned Tomedien, and the former Rodbearer. Possessing years of experience with the arts of elemental Summoning, he has power to match his wisdom, and is one of the most capable people alive at dealing with the demonic Urakait. He teaches his granddaughter Hiaté Noumou and her older brother Haren Noumou, the next in line to become the Rodbearer, about their history and heritage so they are prepared to take up the legacy. He is a rather stern and serious, but not unkind person, with a softer and warmer side that shows when the demands of his responsibilities allow enough room for it.
Story Summary (Spoilers Beyond This Point)
During a struggle against a group of Urakai, Hiaté's memories are drawn to the teachings of her grandfather, Diestat. She recalls him testing her and her older brother Haren's studies on the history and significance of the Rod of Ulzis, with Hiaté being attentive and answering correctly, while Haren shows little interest, and then aggravation as his sister is praised over him. Haren leaves, and Diestat tells Hiaté not to worry about him, saying that he wanted to talk to her and leading her to a building called the Mushroom Tower. When Hiaté reminds him that the Tower is exclusively reserved for the Rodbearer and their students, Diestat looks at her meaningfully and agrees, bringing her inside.
Diestat bestows Hiaté with a Summoner's staff, and reveals his intentions to train her to be the next Rodbearer instead of Haren, despite tradition, owing to Haren's poor attitude and her far more sincere and dedicated behavior. Hiaté graciously accepts, and Diestat begins her first day of training, starting by showing her his Created, Aquablazen. With a few hitches and bumps along the way, including the immolation of his beard, Diestat teaches Hiaté in the use of several elements, his granddaughter excelling under his tutelage. They finally finish with Hiaté Summoning her first ever Created, resulting in Mopoko. Diestat calls it cuddly while saying it is in part shaped by her nature, to Hiaté's embarrassed indignation.
The next day, Haren comes up to Diestat rudely demanding to know where his sister was, as she didn't come home last night, and also asking what was going on in the Tower. Diestat replies that he was cooking, then retorts by asking Haren if he's afraid of getting upstaged by his sister again. At this point Hiaté returns, and she and Haren walk off. Hiaté admits to Haren that Diestat is making her the next Rodbearer, and shockingly Haren attacks her, becoming possessed by an Urakait. Luckily Diestat shows up with the Rod and uses it to seal the Urakait. He comments on Haren being their first victim when he thought it pointless to prepare for their return, and tells Hiaté her fate is to face them.
Later, Hiaté recounts more of her past for Samuel Boyd, a new friend who fought alongside her against the Urakait. She speaks of her home country, Tomed, being overrun by an army of Urakai, and her grandfather getting her and Haren out of there by bird as fast as possible. Diestat brought them to the entrance of an old escape route through the mountains and into the neighboring country, Squirden, where he said he would stay and hold the Urakait off. Before bidding his grandchildren farewell he Summoned Aquablazen, who gifted an egg containing her child to Hiaté, and Diestat passed the Rod of Ulzis to her, taking her Summoner's Rod in exchange to fight with. He encouraged them to keep hope, then prepared for his final stand to cover their escape.
Hiaté believes her grandfather died that day. As she, Sam, and some of their other friends enter an illegal underground fighting arena to try and recover the stolen Rod, she is unaware that Haren is watching them through a magical orb, and holding her grandfather alive and captive in the sinisterly renovated Mushroom Tower. Haren gloats about the power he now has, remarking that he is aware of his grandfather's 'trump card' and reveling in his shock, before returning to watching events.