Yoto was right the first time when christmas was mentioned, when Masumi asked Yoto what he was doing on the 25th of the month, as it is December, she was inviting him to dinner, but also she was wanting to spend a little special time with him, she wants to monopolize Yoto, but she has the benefit of having a younger sister, so she knows a bit about dealing with the feeling of wanting to have somebody all to herself. Masumi is looking at Yoto as more than a friend, he's not quite a potential mate, but as he's liked by Mana, he's a very strong candidate, and there is no one else around that is close to being more than just a good friend, so she strongly wants to know him better, she doesn't know how much he puts himself down, but that doesn't matter to her anyway, Yoto is the only one who thinks he's not good enough to be around her.
Yoto was right the first time when christmas was mentioned, when Masumi asked Yoto what he was doing on the 25th of the month, as it is December, she was inviting him to dinner, but also she was wanting to spend a little special time with him, she wants to monopolize Yoto, but she has the benefit of having a younger sister, so she knows a bit about dealing with the feeling of wanting to have somebody all to herself. Masumi is looking at Yoto as more than a friend, he's not quite a potential mate, but as he's liked by Mana, he's a very strong candidate, and there is no one else around that is close to being more than just a good friend, so she strongly wants to know him better, she doesn't know how much he puts himself down, but that doesn't matter to her anyway, Yoto is the only one who thinks he's not good enough to be around her.