Kasou Ryouiki no Elysion

Kasou Ryouiki no Elysion (仮想領域のエリュシオン) is a light novel series by Kazuma Jouchi with illustrations by nauribon.

Plot
An incredibly athletic older brother, Tenryu Taiga. A programming genius girl, Tenryu Fuyuki. Siblings separated for 8 years ended up living under one roof again, after facing the problem—a lack of funds for living expanses.

Fuyuki proposes a way to earn money, a core system deeply involved in people's daily lives, a game that awards you money as a prize for defeating malicious bugs in cyber world, the 《Aries》 structure. Taiga after becoming a warrior in the game relying on his inborn senses, is puzzled by the unfamiliar sensation.

One day Saionji Rui, Fuyuki's best friend appears and is attacked by a mysterious bug― "I'll be waiting, my prince." Hybrid fantasy battle of cheating siblings begins here!