Schwarzesmarken: At Ease

Theodor Eberbach looks on as Lise Hohenstein smiles

Theodor Eberbach and his step-sister, Lise Hohenstein, are pilots in the same East German battle squadron during the brutal war against the BETA alien invasion, so they keep an eye out for one another.
From the anime series Schwarzesmarken

Saikin, Imouto no Yousu ga Chotto Okashiinda ga: Sure, I Guess

Yuuya Kanzaki smiles while Mitsuki Kanzaki looks away

Both Yuuya Kanzaki and Mitsuki Kanzaki have difficulty adjusting to each other as stepbrother and stepsister after his dad and her mom get married.
From the anime series Saikin, Imouto no Yousu ga Chotto Okashiinda ga. (Recently, My Sister is Unusual)

Shinmai Maou no Testament: Thou Shalt Be Happy

Basara Tojo, Mio Naruse, and Maria Naruse standing outside in front of a building

When his dad suddenly remarries, Basara Tojo finds himself with two younger step-sisters, Mio Naruse (red hair) and Maria Naruse (white hair), who happen to be actual demons.
From the anime series Shinmai Maou no Testament (The Testament of Sister New Devil)

Fate/stay night: Children of the Magus Killer

The Holy Grail War pits master and servant against master and servant, and in this fifth conflict, two of those masters are actually siblings. For those who already know who they are (or for those who simply don’t care), click the logo above or click here to see them.
From the anime series Fate/stay night