On 9 February, Mashiro was announced to take part in NIJI Liver mask merchandise.
On 12 February, Mashiro's Valentine and Setsubun 2021 voice pack went up for sale.
On 19 February, Mashiro reached 200,000 subscribers on his YouTube channel.
On 12 March, Mashiro's Springbreak 2021 and White Day 2021 voice pack went up for sale.
On 19 March, Mashiro's Occupation Parody 2021 voice pack went up for sale. He was chosen to be part of the key visual in this voice pack, which was his first.
On 1 April, Mashiro's Cherry Blossom Viewing 2021 voice pack went up for sale.
On 20 April, Mashiro annouced his first solo merchandise for his upcoming birthday. This year the script was written by Kurusu Natsume of Mananatsu.
On 2 May, Mananatsu announced their third merchandise, a folding umbrella.
On 23 June, Mashiro's Before Rain and Tanabata 2021 voice pack went up for sale.
On 2 July, it was announced though NIJISANJI official Twitter account that Mashiro would get his 3D model that would debut on 10 July. His 3D debut was highly iconic due to the narrative it followed and many easter egg references to the horrific objects he had reviewed or explained throughout his Vtuber career.
On 10 July, Mashiro reached 250,000 subscribers on his YouTube channel.
On 21 July, Mashiro's Summer Vacation and Beach day 2021 voice pack went up for sale.
On 2 August, Mashiro was announced to take part in NIJI Literature vol.3 where they would have to do a folklore/short story reading. He was in-charge of reading 文字禍 (Character) by Atsushi Nakajima.
On 20 August, Mashiro's Mountain Hiking Vacation 2021 voice pack went up for sale.
On 17 September, Mashiro's Moon Viewing and Autumn:Sport and Food 2021 voice pack went up for sale.
On 29 September, Mashiro's Good Morning & Good Night 2021 voice pack went up for sale. His voice pack did not have a merchandise release unlike a few of his colleagues.
On 18 October, Mashiro's Autumn Leaf and Autumn Art 2021 voice pack went up for sale.
On 19 November, Mashiro's Seasonal Vol 1 & 2 2021 voice pack went up for sale.
On 16 December, Mashiro reached 300,000 subscribers on his YouTube channel.
On 22 December, Mashiro's December Seasonal Vol 1 & 2 2021 voice pack went up for sale.