Eight

Eight is an orange robot in love with his creator. He was created to be the ultimate nursing robot by the Sanzenin Technology Division. He is waterproof and equipped with "nursing missiles" and rocket boosters. Eight's downfall is his quick temper. He snaps after being called "ugly" and seeks revenge after he is defeated. Through his dialog, he reveals that he only desires revenge in order to prove himself to the one he loves: his creator. Sadly, Shiori has a habit of being totally dismissive of him, going as far as telling him she made a "mistake" in putting him in line for incineration when he actually needed to be trashed in a more appropriate category. Nonetheless, he eventually gets a reprieve after his latest upgrade, when he becomes Shiori's boyfriend after finally confessing to her. Eight receives an upgrade before each appearance. He is upgraded to v8.1 after his first defeat, upgraded to v8.2 before meeting Hayate in the amusement park, v8.3 after he becomes a couple with Shiori, and upgrades his form after Shiori is transferred to Hakou Academy. In the anime, Eight upgrades himself to v8.1 after he steals the control chip from Nursing Robot Nine and upgrades to 8.2 as his second form, but he is reverted back to v8.1 after he is beaten by Yukiji and Hayate.

(Source: Hayate no Gotoku! Wiki)