Sword Art Online - Kirito's Gun Gale Wars summary:

Having won a photon sword in a mini game, Yui decided that it would be the perfect gift for Kirito. However, convinced that a present is more impactful when it's delivered as a surprise, Yui enlisted the help of Asuna and the other girls. The girls would face Kirito in battle during a new GGO event and create an opportunity for the perfect surprise: using slime guns to blind him during the fight, thus allowing Yui to present her gift to the unsuspecting Kirito just as he regains his vision. However, Yui did not foresee one thing: that her surprise gift will have to compete in impactfulness with Kirito's mastery at getting himself into all kinds of ecchi situations...