Itsudatte My Santa!

Itsudatte My Santa! (いつだってMyサンタ!?, translating literally to Always My Santa!) is a manga series by Ken Akamatsu, published before his better known work, Love Hina, was serialized. It stars a boy named Santa who hates Christmas, due to being born on Christmas Eve.

Contains examples of:

 * Accidental Pervert: It's not actually Santa's fault, but he does get to see Mai naked...and get punished for it.
 * A-Cup Angst: Although not nearly as pronounced as other examples, Mai is offended when Santa teases her about her chest.
 * Adaptation Expansion: The manga only tells the story told in episode one, and only has two characters, Mai and Santa. The anime adds a second episode and introduces the characters of Sharry, MaiMai, and Miss Noel.
 * Annoying Younger Sibling: MaiMai.
 * Beach Episode: The beginning of episode 2.
 * Big Eater: Sherry (and MaiMai) devour a mountain of cantaloupes while Sherry Info Dumps she and Sherry's relationship.
 * Bokukko (In the Japanese version, Mai uses "ore" when referring to herself in her adult form.)
 * Delinquents - A recurring group of characters are a gang leader and his entire gang, carrying food that inevitably gets smashed.
 * Everyone Is Christian At Christmas, despite being native Japanese citizens.
 * The Faceless: Mineko, the girl Santa has a crush on, is always shown from behind when Santa goes to her party, although this doesn't seem to be entirely intentional.
 * There is one shot of her face, although it's from very far away and hard to make anything out.
 * Fan Service - As this is an Akamatsu work, there is a lot.
 * Shower Scene: Mai takes a shower when she gets to Santa's apartment, which ends with her bursting out and giving Santa a full view of everything.
 * Gainaxing - Closely watch how Sherry's chest moves of its own accord, which shouldn't be hard.
 * Genki Girl: Mai
 * Hair of Gold - Sherry
 * Hot-Blooded - Sherry, again.
 * Idiot Hair: Again, a staple of Ken Akamatsu's work, the female lead has a pair of antennae-like hairs standing on end.
 * Incoming Ham - "Ho, ho, ho! Long time no see, Mai and MaiMai!"
 * Manic Pixie Dream Girl: Mai to Santa.
 * Paper Fan of Doom: Mai unleashes one of these at least once.
 * Parental Abandonment: Santa suffers from this, to a certain extent.
 * The Rival: Sherry to Mai.
 * Santa's Existence Clause - Not only does Santa exist, but he is actually several hundred cute teenage girls!
 * Sexy Santa Dress: Worn by Mai in her Santa form and in the Eyecatch.
 * Shower of Awkward: Santa sees Mai completely naked during her shower (although he's fully dressed).
 * Sugar and Ice Personality - The plot is partially centered around Mai getting Santa to come out of his shell.
 * Transformation Sequence: When Mai transforms into Santa Claus.
 * True Meaning of Christmas: According to Mai, this is a celebration of the birth of...the protagonist, Santa.
 * Tsundere (Sherry)
 * Mai also has shades of this.
 * Tsurime Eyes - Sherry's eyes notably slant upward.
 * Unlucky Everydude: Santa, as per the usual for Akamatsu's protagonists.